Learning Science
The Forgetting Curve
Why we forget most of what we learn within days — and how spaced reviews flatten the curve. The science behind SkillPark.
In the 1880s, psychologist Hermann Ebbinghaus memorized lists of nonsense syllables and then tested himself at intervals. What he found became one of the most replicated results in psychology: memory decays fast, and predictably.
The shape of forgetting
Without review, retention falls off a cliff:
- Within 20 minutes, meaningful loss has already started.
- Within a day, most learners retain well under half of new material.
- Within a week, an unreviewed lesson is mostly gone.
This is why a class that nodded along on Monday looks blank on Friday. Nothing went wrong — that’s just what unreviewed memory does. Teaching quality can’t fix it; only review timing can.
The fix: interrupt the curve
Each time you successfully recall something just as you’re starting to forget it, two things happen:
- Retention jumps back to ~100%.
- The new curve decays more slowly than the last one.
After a handful of well-timed reviews, the curve is nearly flat — the memory has moved into long-term storage. The reviews must be spaced out, though: recalling something five times in one evening flattens nothing (your brain never got the chance to start forgetting), while the same five recalls spread over a month can secure the memory for a year.
What SkillPark automates
The theory is old and solid; the hard part has always been logistics. Which of your 400 cards is each person about to forget today? No teacher can track that per student, and self-learners almost never do it by hand.
That scheduling is exactly what SkillPark does. Every card carries its own decay estimate, updated each time you answer, via the SM-2 spaced-repetition algorithm. Your daily review session is simply “the cards whose curves are about to dip” — nothing more, nothing less.
Further reading
- Ebbinghaus, H. (1885). Memory: A Contribution to Experimental Psychology.
- Murre, J. & Dros, J. (2015). “Replication and Analysis of Ebbinghaus’ Forgetting Curve.” PLOS ONE — a modern replication confirming the original result.
- Cepeda et al. (2006). “Distributed practice in verbal recall tasks.” Psychological Bulletin — the meta-analysis on spacing effects.