Concept
Desirable Difficulties
Desirable difficulties are learning conditions, such as testing yourself, spacing sessions apart and mixing problem types, that make practice feel slower and harder in the moment but build stronger, longer-lasting and more flexible memory than easy, fluent study.
Psychologist Robert Bjork coined the term to name a trap most of us fall into. Rereading notes or doing fifteen problems of the same kind in a row feels productive because your performance during practice is high. But that performance measures how easy the material feels today, not what you will still know next month. Your brain does extra work in three situations: when you have to pull an answer from memory, when you revisit material just as it starts to fade, and when you must decide which method a problem needs. That effort is what makes knowledge stick. In blocked practice, the method is chosen before you read the question. Mixed practice makes you do the choosing. The catch is in the word 'desirable.' The difficulty has to be one you can overcome with effort. Without the basics, it is just confusion. Expect your practice scores to dip. That dip is not failure.
A real-life example
Dan, a junior analyst studying for a finance certification, used to do twenty questions on one topic per evening. He switched to mixed sets covering four topics. His practice accuracy fell from 85% to 65%, and he almost switched back. Three weeks later he sat a mock exam where nothing was labelled by chapter. He recognised which approach each question needed far faster than before and finished with his best score yet.
How to use it
- 1Open each study session by writing down, from memory and in three minutes, everything you recall from the last one. Then check it against your notes.
- 2Once you can do each method on its own, mix problem types within a session instead of working through one type in a block.
- 3Spread reviews across days rather than cramming them together. Treat a lower score as effort paying off. Only step back to the basics if you cannot solve anything at all.