You learn a new word, feel sure of it, and it's gone by the weekend. That isn't a personal failing — it's one of the most reliable findings in all of psychology. It even has a shape: the forgetting curve.
Where the curve comes from
In the 1880s, the German psychologist Hermann Ebbinghaus ran a famously tedious experiment on himself. He memorized lists of nonsense syllables — "WID," "ZOF" — then measured how much he could recall after an hour, a day, a week. Plotting the results gave a downward curve that's steep at first and then flattens: you lose the most in the first 24 hours, then the decline slows.
The headline finding is uncomfortable: without review, you forget the majority of new material within a day or two. Most of what you "learned" in a study session is already leaking away by the next morning.
The myth to avoid
You'll see confident claims online that you forget "exactly 50% in an hour" or "70% in 24 hours." Treat the precise numbers with suspicion — they come from one person memorizing meaningless syllables. Real words, in context, with meaning attached, decay more slowly. The shape of the curve is what matters and what's been replicated countless times, not the exact percentages.
Forgetting isn't the enemy. A little forgetting is what makes the next review work.
Why a little forgetting helps
This is the counterintuitive part. If you review a word while it's still perfectly fresh, your brain does almost no work and the memory barely strengthens. If you wait until you've half-forgotten it, retrieving it is effortful — and that effort is exactly what tells your brain "this matters, keep it." Psychologists call this desirable difficulty.
So the optimal moment to review is near the bottom of the curve, just before it hits zero. Too early wastes the review; too late and you're relearning from scratch.
Flattening the curve
Here's the good news hidden in Ebbinghaus's data: each review resets and flattens the curve. After the first successful recall, you forget more slowly. After the second, slower still. Stack a few well-timed reviews and the curve becomes nearly flat — the word is now in long-term memory and needs only occasional refreshing.
That stacking is precisely what spaced repetition automates: it predicts where you are on each word's curve and surfaces it at the bottom, not before.
What this means for your study
- Don't re-read — retrieve. Looking at a word again sits high on the curve and barely helps. Recalling it from memory is what counts.
- Space your reviews. One review today plus one in three days beats two reviews today.
- Let the easy ones drift. Words you know well should come back rarely; spend your effort on the shaky ones.
Putting it to work
You can track all of this on paper, but it gets unwieldy past a few dozen words. LexiNest keeps each word's curve for you and resurfaces it at the right moment — pick a language and start free: German, Spanish, Polish.
Frequently asked questions
How fast do we really forget?
Steeply at first — most loss happens within the first day — then more slowly. Exact percentages vary by material; meaningful words in context fade slower than nonsense syllables.
Can you stop forgetting completely?
Not entirely, and you don't need to. A handful of well-spaced reviews flattens the curve enough that a word stays usable with only rare refreshers.