Desirable (and Undesirable) Difficulties: Tuning Body and Mind for Optimal Learning

Must Learning Be Bitter? #

We have discussed many methods and contents of learning; in this lecture, let’s talk about the posture. Tell me, does learning require suffering?

Folk wisdom believes that learning must be bitter: sayings like “tying one’s hair to the roof beam and jabbing one’s thigh with an awl” (to stay awake) or “the sea of learning is boundless, making hardship your boat” suggest that if it isn’t accompanied by some degree of physical torment and mental suppression, it is not called learning, but “playing.” Coupled with the steady-state survival concept that treats suffering as a virtue, people not only praise suffering but also actively seek it out, forcing hardship upon themselves even when there is none.

When I was in school, China had already progressed a lot. I never dreamed that today’s China would turn out like this: students are called up early in the morning for morning runs, they have to carry a book to memorize while running, the ten-minute breaks between classes are canceled, they can’t even have a peaceful lunch, they suffer from chronic sleep deprivation, and they are subjected to public-shaming style frustration education…

Are these really the necessary conditions for getting good grades? Or are the kids who learn easily, sleep well, and feel happy just spoiled brats?

A 2024 systematic review summarizing 439 studies estimated that the detection rate of depressive symptoms among Chinese children and adolescents had reached 26.17% [1]! This situation is highly abnormal, and it is precisely caused by the academic pressure of unnecessary hardship. Why dare I say this?

A study targeting 200,000 primary and secondary school students found [2]: after the State Council introduced the “Double Reduction” policy in 2021—that is, reducing homework burdens and off-campus tutoring—students’ sleep duration increased, and their feelings of depression and anxiety decreased. A study of Shenzhen students found [3]: the relationship between homework duration, sleep, and mental health is not simply “more homework means worse health,” but there is a threshold: it only begins to deteriorate after crossing that threshold.

Most crucially, sacrificing sleep to do homework is undesirable even purely from the perspective of academic performance—a study of Shanghai students found: the optimal sleep duration for academic performance is 8 hours per day [4].

For a bunch of primary and secondary school students, what learning material could possibly be so important that they have to sacrifice sleep? Forcing unnecessary hardship is a foolish form of self-affection; it is passing off the wear and tear of the nervous system as the growth of cognitive abilities.

A Neuroscience Perspective: Two Checkpoints to the Brain #

Let’s consider this from a micro-scale. For a piece of knowledge to enter the brain, two levels of problems must be solved: the first level is “can it be learned in,” meaning at this moment, can this thing be noticed by you, and does your brain judge it worth writing; the second level is “can it be understood,” meaning do you have the ability to encode it into usable knowledge.

Whether it can be taken in happens on a time scale of milliseconds to a second. The brain makes a rapid value judgment, but it doesn’t ask whether the problem is hard or if the task is bitter; rather, it asks whether this thing is new, whether it is worth caring about, and whether there is a reward. If the answer is positive, the brain releases dopamine, making the hippocampus willing to open its doors so the information can be remembered.

This is why it is said that “interest is the best teacher,” and why curiosity is best at capturing learning attention. It is also why some children just cannot learn classroom knowledge well, but they can pick up things like playing video games instantly. Research has found that if a question can genuinely arouse curiosity, a person’s memory of the answer to this question after learning is usually much better [5], because dopamine buffs the hippocampus.

For the level of whether it can be understood, the brain’s most important metric is “arousal,” which is the degree of tension and excitement, primarily regulated by norepinephrine [6]. If the arousal is too low, one is absent-minded or even feels sleepy, which naturally leads to poor learning; but if the arousal is too high, one becomes nervous and panicked, which also makes learning impossible.

Learning requires a moderate level of arousal. The ideal emotional state is a kind of controllable excitement: I know this is important, I am a bit hyped up, I am very engaged right now, but I am not afraid.

If you are already very sleepy and need to “tie your hair to the beam and jab your thigh” to stay awake, then your state is not suitable for learning. When parents use high pressure to force children to do homework, even beating or scolding them on the side, that is even less of a learning state.

The reality is that high-pressure stimulation directly hits the brain’s prefrontal cortex, weakening its control [7]. Threats and judgments reduce working memory performance and interfere with the activity of relevant brain regions [8]. Once pressure goes overboard, the prefrontal cortex tends to go offline, resulting in impaired flexible reasoning, working memory, and cognitive control, making people more rigid and short-sighted… that state is more like avoiding danger than learning. Simply put, fear creates obedience, not understanding.

Learning is not manual labor; it’s not something where you can just grit your teeth and hold on a bit longer, or work harder if whipped. Learning is a highly delicate brain activity that requires a certain atmosphere. The most conducive emotional recipe for learning is:

A foundation of a sense of security + ignited by curiosity + accelerated by moderate pressure.

But learning is, after all, not playing. You can’t become a top scorer in the college entrance exam just by swiping short videos; you must overcome some difficulties.

So what kind of difficulties?

Desirable Difficulties: Resistance That Benefits Learning #

The answer is “Desirable Difficulties.” This mental model was proposed in the 1990s by Robert Bjork, a psychologist at the University of California, Los Angeles (UCLA) [9].

Desirable Difficulties are resistance that is beneficial to learning.

Bjork and his wife, Elizabeth Bjork, conducted extensive research together, and one of their most important insights is: you must separate “performance” from “learning” [10].

For example, today’s homework is ten practice questions. Xiao Ming takes them and finishes them quickly. His parents are very happy, saying this child really loves learning. But that wasn’t learning; that was just performance. Those questions had no difficulty for him whatsoever, and he learned nothing from that homework. By the same token, if you read a textbook over and over a hundred times, you will read it very fluently, and this fluency will give you the illusion of “I have mastered it,” but that isn’t learning either.

Actually, we have discussed “Deliberate Practice” before, so you already know this principle: practicing in the “learning zone” is what constitutes learning. The Bjorks emphasized from a micro perspective that resistance—that is, “Desirable Difficulties”—while making your short-term performance worse, can make your long-term memory and transfer ability stronger.

There is a lot of experimental research on “Desirable Difficulties.” Here we list the three most practical operational techniques:

First, Retrieval Practice. That means taking more quizzes. One quiz is much more effective than rereading a book, because you have to think hard, which is a desirable difficulty.

Second, Spacing. Instead of cramming for 5 hours in one day, it’s better to study for 1 hour a day for 5 consecutive days. Every time you pick up the book again and recall the point where you “disconnected” the previous day, this sense of forgetting is a desirable difficulty. When you concentrate on work, you don’t want to be interrupted, but for learning, being interrupted once a day is actually a good thing. While you are struggling to recall what you learned last time, your brain is strengthening synaptic connections.

Third, Interleaving. Do not just study math this week and only English next week; you should mix different subjects or different contents of the same subject and interleave them. The sense of confusion brought by switching can deepen memory and force the brain to identify the deep structure of the problem, judging “what category is this question really,” rather than relying on muscle memory.

Actually, there is another method which is to let students “guess first, learn later”: give them some new content to try on their own first, and then have the teacher explain it. But as we said earlier when discussing “Cognitive Load Theory,” this teaching method is too advanced and often less effective than direct instruction.

Simply put, desirable difficulties make students grapple with the content they are learning, tossing and turning within the bounds of intrinsic load; whereas undesirable difficulties apply pressure from the outside, adding worthless extrinsic load to students, making them grapple with fatigue, interference, and threats.

Moreover, desirable difficulties do not increase anxiety. Studies have found [11] that 72% of middle and high school students reported that retrieval practice made them less nervous during formal exams.

Exercise: A Hack to Briefly Boost Brainpower #

Speaking of which, you might wonder: if there are suitable and unsuitable states for learning, can I do something else to improve this state? I don’t want to tie my hair to the beam or jab my thigh; I want to use scientific methods to improve my brainpower a bit more and make my learning effects a bit better. Is that possible? Yes.

One is exercise. For instance, if you are about to take an exam or learn something difficult and want to boost your brainpower in a short time, the best method isn’t drinking coffee, but going out for an acute bout of moderate-intensity exercise for about 20 minutes. Things like brisk walking, jogging, climbing stairs, jumping rope, or doing a few sets of squats.

Exercise can not only elevate you from a lethargic state to a competitive state, increasing arousal, but it also produces lactic acid. Studies have shown that lactic acid produced by exercise can cross the blood-brain barrier to directly provide energy to neurons, and even stimulate the secretion of a substance called “Brain-Derived Neurotrophic Factor” (BDNF). This neurotrophic factor is known as “fertilizer for the brain,” which can promote the growth of neurons and synaptic connections, thereby enhancing learning and memory [12].

Of course, you can’t expect to run two laps and come back instantly much smarter. The effect is not that massive, but it is very reliable and consistently present [13].

So letting children go out to the playground for the 10-minute break between classes, even if they come back sweating, is not a waste of time; it is promoting learning.

Sleep: The Brain’s Cleaning and Archiving Process #

Another is sleep. One of the biggest cognitive errors of ancient teachers was viewing sleep as laziness. Actually, sleep is a necessary process of learning.

This is because sleep is not just rest; it is the brain’s “cleaning and archiving” time. When you sleep, the brain’s glymphatic system clears metabolic waste (such as amyloid-beta)—this physical flushing process of “cerebrospinal fluid brainwashing” occurs almost exclusively during sleep. At the same time, your hippocampus transcribes daytime short-term memories to the cerebral cortex, turning them into long-term memories. Even sleeping and dreaming are rehearsals of the knowledge learned during the day.

Scientists today pay increasingly more attention to sleep, and our “Elite Daily Course” column has already covered far too much research related to sleep—but the role of knowledge is limited. The current problem is that adolescents are clearly sleep-deprived.

If you sleep less than 6 hours a day, you risk accumulating cognitive damage, which hurts long-term memory. And adolescents need more sleep than adults. Adults should sleep at least 7 hours a day, and the research consensus recommends 8 to 10 hours of sleep per day for adolescents [14]. This means schools should cancel both late evening and early morning study sessions, assign less homework, and let children sleep more.

No coach would ever make their athletes sleep less and call it tempering their willpower. So why don’t teachers and parents create conditions for children to sleep more? Visionaries advocate that middle school should not start earlier than 8:30 AM.

Then you might ask, what if the homework cannot be finished? If it can’t be finished, it should be boycotted. In fact, there is only so much we need to learn; as long as the methods are right, there is absolutely no need to stay up late. Learning is about intensity, not duration, and not about how many test papers you have completed. True deliberate practice is high-intensity, and usually, guaranteeing three or four hours a day is enough; the rest is auxiliary time, where you should relax when it’s time to relax, and sleep when it’s time to sleep. If you cannot learn those things well under the premise of ensuring adequate sleep, inadequate sleep will only make you learn even worse.

When people are sleepy, they should sleep, not poke themselves with needles.

Embodied Cognition: The Body as Part of Thinking #

If you want to go a step further and use your body to help your brain think, you have to use the theory of “Embodied Cognition” from modern neuroscience and psychology. We mentioned embodied cognition in the previous lecture when talking about “Tacit Knowledge”; this is a cognitive style more characteristic of humans.

Embodied cognition implies that the body’s actions, posture, sense of touch, and spatial orientation all participate in the brain’s modeling process. “Understanding” is not just a symbolic computation happening within the brain. The body is not just a power supply servicing the brain’s CPU; the body is part of thinking [15]. Often, it’s not that you figure it out first and then act; rather, once you start acting, your brain begins to understand.

Let’s discuss four learning techniques based on embodied cognition:

First is doing physical actions. When doing math problems, you can gesture in the air with your hands; when learning geometry, you can trace the direction of angles and edges with your hands. Research shows that, especially for children, using hands in math classes can strengthen problem-solving abilities and conceptual understanding [16]. When learning new vocabulary in a foreign language class, if it’s a verb, it’s best to engage the whole body and perform the action. When studying anatomy and physiology, pointing at and tracing models or pictures can help deepen understanding and memory [17].

These actions are not decorations; they are unburdening your working memory.

Second is handwriting. A large number of studies show that taking handwritten notes deepens understanding and memory better than typing [18]. The problem with typing is that it’s too fast and too easy; you act more like a stenographer. Handwriting is slower, so you are forced to reorganize your own words and translate the content into your own syntax—this “slowness” is actually a desirable difficulty. Research has found that brain connectivity patterns are broader and more complex during handwriting than typing; handwriting activates a richer sensory-motor integration process [19].

Third is reading paper books. I often read e-books and always look at things on my phone, but if you are reading serious content, especially if there is time pressure and you need rapid mastery and deep understanding, you had better read the paper version [20].

This is because paper provides stable spatial coordinates. The content in a book has a natural sense of location—how far into the book it appears, whether it is in the upper left or lower right corner of the page. This sense of location is not redundant information, but where you anchor your memory: don’t forget that the hippocampus, which is responsible for long-term memory in the brain, was originally used for remembering spatial locations and navigation.

Therefore, for the harder things, especially those that require your annotations and underlining, it’s best to use paper. Another approach is to use a large monitor for your computer or provide a few more screens, which can also increase the sense of location.

Fourth is to stand up and walk a few steps if you can’t think of an answer. Walking can help you expand your thinking and generate creative ideas [21].

Walking can slightly increase the brain’s arousal, making you a bit more alert. Walking can break hyperfocus, because sometimes the reason you can’t figure something out is that you are staring too intently and only see the tiny point right in front of you. Walking allows you to see other paths and associate new solutions. If you walk in a relatively quiet, natural physical environment, it can also improve your mood and stress conditions.

As carbon-based biological organisms, knowledge is not directly downloaded into our brains; knowledge is a structure that “grows” with the participation of our bodies.

Treat Learning Like an Athlete #

I hope that all you “learners” can treat your bodies and brains like athletes do. You are carbon-based biological organisms; you do not just plug in and work. You have different states. Some states are better suited for learning, and some are suited for resting. People in cultivation novels often have to burn incense and bathe; athletes must warm up, manage pressure, and get into the zone before taking the field. We, too, need a bit of a ritual.

A basic athlete-style learning workflow looks something like this:

• Before learning something new, ignite your curiosity with a question.
• Before engaging in serious mental work, exercise for 10–20 minutes to slightly increase arousal.
• When learning, rely mainly on retrieval, spacing, and interleaving, not on rereading.
• For difficult concepts, try to handwrite; for deep reading, try to read on paper.
• Write sleep into your learning plan, not into your confession book.

The most important point of all: learning requires desirable difficulties, but not suffering. Learning is about training you, not consuming you. A master learner should keep their body and mind in an agile, rather than rigid, state.

Gemini praises with a poem:

Do not believe that tying one’s hair makes hardship a boat, Vainly boiling one’s heart’s blood, when will it end? The foolish mistakenly drink unprovoked bitterness, Artificial acts only add unresolved sorrow. Wondrous truths rely entirely on excellent inspiration to guide them, Great talent is more likely to remain in dreams. Today I break the delusion and pass on the true essence, Just ride the long wind and stand at the crest of the waves!

GPT also says:

The whole hall still worships the ascetic sect, Mistaking devastation for a sacred merit. Trapped to the point of a confused mind, how can one see reason? Crushed into wood and stone, how can one be enlightened? True learning fundamentally starts from where doubts arise, A flexible mind leans towards the moments of wakefulness to connect. If you teach latecomers to seek the true formula, Do not look to corporeal punishment to ask for diligent effort.

注释

[1] Zhou, Jia, et al. “Prevalence of Depressive Symptoms among Children and Adolescents in China: A Systematic Review and Meta-Analysis.” Child and Adolescent Psychiatry and Mental Health 18 (2024): 150.

[2] Wang, D., et al. “Changes and Relevant Factors in Depressive and Anxiety Symptoms among Chinese Adolescents after the ‘Double Reduction’ Policy: A Repeated Cross-Sectional Survey with a Nested Longitudinal Subsample.” Journal of Affective Disorders 365 (2024).

[3] Liang, Kaixin, Diyang Qu, Anni Zhu, and Xinli Chi. “How Much Homework Is Too Much? Identifying Thresholds for Adolescent Sleep and Mental Health by School Stage.” Journal of Affective Disorders 389 (2025): 119636.

[4] Wang, Maohua, et al. “Sleep Duration and Subject-Specific Academic Performance among Adolescents in China.” npj Science of Learning 10 (2025): 71.

[5] Fandakova, Y., & Gruber, M. J. (2021). States of curiosity and interest enhance memory differently in adolescents and in children. Developmental Science, 24, e13005.

[6] O’Callaghan, Claire. “Noradrenaline Drives Learning across Scales of Time and Neurobiological Organisation.” Trends in Cognitive Sciences (2025).

[7] Arnsten, Amy F. T. “Stress Signalling Pathways that Impair Prefrontal Cortex Structure and Function.” Nature Reviews Neuroscience 10 (2009): 410–422.

[8] van Ast, Vanessa A., et al. “Brain Mechanisms of Social Threat Effects on Working Memory.” Cerebral Cortex 26, no. 2 (2016).

[9] Bjork, Robert A. “Memory and Metamemory Considerations in the Training of Human Beings.” In Metacognition: Knowing about Knowing, 185–205. MIT Press, 1994.

[10] Bjork, Elizabeth L., and Robert A. Bjork. “Making Things Hard on Yourself, but in a Good Way: Creating Desirable Difficulties to Enhance Learning.” In Psychology and the Real World, 56–64. New York: Worth, 2011.

[11] Agarwal, Pooja K., et al. “Classroom-Based Programs of Retrieval Practice Reduce Middle School and High School Students’ Test Anxiety.” Journal of Applied Research in Memory and Cognition 3, no. 3 (2014): 131–139.

[12] El Hayek, Lauretta, et al. “Lactate Mediates the Effects of Exercise on Learning and Memory through SIRT1-Dependent Activation of Hippocampal BDNF.” Journal of Neuroscience 39, no. 13 (2019): 2369–2382.

[13] Garrett, Jordan, et al. “A Systematic Review and Bayesian Meta-Analysis Provide Evidence for an Effect of Acute Physical Activity on Cognition in Young Adults.” Communications Psychology 2 (2024): 82.

[14] Paruthi, Shalini, et al. “Recommended Amount of Sleep for Pediatric Populations: A Consensus Statement of the American Academy of Sleep Medicine.” Journal of Clinical Sleep Medicine 12, no. 6 (2016): 785–786.

[15] Barsalou, Lawrence W. “Grounded Cognition.” Annual Review of Psychology 59 (2008): 617–645.

[16] Goldin-Meadow, Susan, Susan Wagner Cook, and Zachary A. Mitchell. “Gesturing Gives Children New Ideas About Math.” Psychological Science 20, no. 3 (2009): 267–272.

[17] Macken, Lucy, and Paul Ginns. “Pointing and Tracing Gestures May Enhance Anatomy and Physiology Learning.” Medical Teacher 36, no. 7 (2014): 596–601.

[18] Mueller, Pam A., and Daniel M. Oppenheimer. “The Pen Is Mightier Than the Keyboard: Advantages of Longhand Over Laptop Note Taking.” Psychological Science 25, no. 6 (2014): 1159–1168.

[19] Van der Weel, F. R. Ruud, and Audrey L. H. Van der Meer. “Handwriting but Not Typewriting Leads to Widespread Brain Connectivity: A High-Density EEG Study with Implications for the Classroom.” Frontiers in Psychology 14 (2024): 1219945.

[20] Delgado, Pablo, Cristina Vargas, Rakefet Ackerman, and Ladislao Salmerón. “Don’t Throw Away Your Printed Books: A Meta-Analysis on the Effects of Reading Media on Reading Comprehension.” Educational Research Review 25 (2018): 23–38.

[21] Oppezzo, Marily, and Daniel L. Schwartz. “Give Your Ideas Some Legs: The Positive Effect of Walking on Creative Thinking.” Journal of Experimental Psychology: Learning, Memory, and Cognition 40, no. 4 (2014): 1142–1152.