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Most students treat forgetting as the enemy. You learn a chapter, a week later half of it seems gone, and the work feels wasted. Robert Bjork, a psychologist at UCLA who works with Elizabeth Bjork, argues something more useful: some forgetting is what makes the next round of study count.
The idea comes from a framework the Bjorks called the New Theory of Disuse, published in 1992. Here is what it says and how to turn it into a revision routine.
What are storage strength and retrieval strength?
In a 2023 chapter published by the American Psychological Association's Division 2, Elizabeth and Robert Bjork explain that every item in memory has two strengths:
Storage strength: how well learned the item is and how interconnected it is with related things in memory.
Retrieval strength: how easily you can reach it right now, given the cues available.
Their examples make it concrete. An address you have lived at for years is high on both. The address of a shop you visited for the first time this morning is easy to recall today but has little storage strength. The name of your best friend from primary school has high storage strength but low retrieval strength. And a lecture you didn't understand is low on both.
The theory assumes that storage strength, once built, is never lost. Retrieval strength rises and falls with recency and with the cues around you.
Why can forgetting help learning?
What is new in the theory, the Bjorks write, are its assumptions about the two strengths and how they interact. The higher an item's current retrieval strength, the smaller the gain in storage strength when you restudy or retrieve it. In their words, "forgetting (loss of retrieval strength) can enhance learning (the gain in storage strength)."
So revising a topic you read ten minutes ago feels smooth but adds little. Revising it after you have partly forgotten it feels harder, and builds more lasting learning. That is why spacing and variation help, and why the Bjorks describe forgetting as the "friend of learning."
The theory adds one more assumption: retrieving something is a more powerful event for both strengths than restudying it. Recalling a formula from memory does more than reading it again.
Why does the better method feel worse?
In the same chapter, the Bjorks note that spacing and interleaving can make learning seem slower, while massing and blocking make performance improve quickly. That is one reason students like rereading straight after reading: familiarity feels like understanding, which they call an "illusion of comprehension."
They add a caution. A difficulty is desirable only if you can respond to it successfully. If you lack the background knowledge to attempt a retrieval, it becomes an undesirable difficulty. Testing yourself on a chapter you never understood won't help. First understand it, let it fade a little, then retrieve.
A revision plan for one chapter
Here is one way to apply the theory to a JEE or NEET chapter, say current electricity, over three weeks:
Day 1, learn for understanding. Study the chapter and solve a short set of problems with help. End by writing the key ideas from memory.
Day 2 or 3, first retrieval. Before opening your notes, write Kirchhoff's laws, the balanced Wheatstone bridge condition and one worked problem from memory. Then check and correct.
In between, study something else. The Bjorks suggest covering a related topic before returning to the first one, which adds spacing without losing time.
Day 7, mixed problems. Solve problems from this chapter mixed with problems from the previous one, without chapter labels.
Day 21, cold test. A timed set with no notes. Whatever you miss goes into an error log for the next round.
If each round feels harder, that is expected. Keep gaps long enough that recall takes effort, but short enough that you can still recall. For a full four-week schedule, see our spaced revision plan, and for the Bjorks' wider work, desirable difficulties applied to daily study.
Where Fermi fits
This plan needs two things that are easy to lose track of: knowing when a topic has faded enough to revisit, and finding problems at the right level. For JEE Main and Advanced, Fermi Testprep offers adaptive mocks and a study plan that updates based on mastery, so revisits follow what you know rather than a fixed calendar.
Take yesterday's topic and, before you look at your notes, write down everything you remember.
