The one-sentence version
Spaced repetition means reviewing something at growing intervals — today, then in three days, then in a week, then in a month — instead of reviewing it many times in one sitting.
That is the whole idea. Everything else is detail about the gaps.
Why the gaps do the work
Learn a word today and you will still have it tomorrow. Leave it a fortnight and it is mostly gone. Memory decays steeply at first and then flattens out — the shape usually called the forgetting curve.
Reviewing interrupts that decay. But when you review changes how much good it does, and this is the part that surprises people:
- Review too early and recalling the word is effortless. Effortless recall teaches you almost nothing. It feels great and does very little.
- Review too late and you have genuinely forgotten. You are not reinforcing a memory, you are learning the word again from scratch.
- Review in the narrow window between the two — when you almost can’t remember it, and then do — and the memory resets and decays more slowly next time.
Difficulty is not a side effect of good studying. It is the mechanism. A review that feels hard is the one that worked.
Why you can’t time it yourself
Here is the awkward part. The window where recall is hard-but-possible is different for every card, and it moves after every review. The word you nailed today needs a longer gap than the one you fumbled. Multiply by four hundred cards and you have a scheduling problem no person can hold in their head.
Worse, your intuition actively misleads you. Material you recognise feels learned, so you skip it — and recognition is exactly the feeling that does not predict recall. Left to ourselves, we review what feels comfortable and avoid what feels difficult, which is precisely backwards.
Which is why software does it
A spaced-repetition scheduler is doing something quite modest: keeping one number per card — when to show it next — and adjusting that number based on how the last review went. Comfortable recall, longer gap. Hesitation or a miss, shorter gap.
In Toly there is nothing to configure about this. No intervals to set, no queue to build, no parameters to tune after reading a forum thread about them. You set a daily minutes goal, open the app, and answer what is due. The cards that need you show up; the ones that don’t stay out of the way.
That is the deal spaced repetition offers: give it honest answers about how each review went, and it will spend your ten minutes better than you would have.