What spaced repetition actually does

Spaced repetition gets described as "reviewing at increasing intervals," which is true and tells you nothing about why it works or how to use it.

Here is the useful version.

Forgetting is scheduled, not random

After you learn something, your ability to recall it decays. Not instantly, not evenly - it drops fast at first, then levels off.

The important part: every successful recall flattens the curve. Remember something on day two and you will still have it on day five. Remember it on day five and you might have it for two weeks.

So the question is not "how often should I review?" It is "when am I about to lose this?" Reviewing earlier than that wastes the repetition. Reviewing later means relearning from scratch.

The interval is the whole mechanism

A spaced repetition system tracks, per card, how close you are to forgetting, and shows it just before you would.

In Encodr that looks like a ladder. Get a card right and it climbs:

1 day, 2, 5, 7, 10, 14, 21, 30, 45, 60, 90.

Get it wrong and it drops back down. Nothing else about the card matters - not how long you stared at it, not how confident you felt.

The effect compounds. A card you have answered correctly six times costs you a few seconds every couple of months. A card you keep missing comes back tomorrow. Your time automatically flows to the things you do not know.

Why a 400-card deck is not 400 cards of work

This is the part people do not believe until they see it.

If you had to review every card every day, 400 cards would be unmanageable. But most cards are not due most days. Once a deck matures, the daily load settles to a small fraction of it - the new cards, plus whatever you are currently failing.

The deck gets bigger. The daily session does not.

What it does not fix

Spaced repetition schedules recall. It does not:

• Make bad cards good. A card asking you to recall a whole paragraph will fail no matter how well it is scheduled. One fact per card.
• Teach you something you never understood. Memorising a definition you cannot use is still memorising a definition you cannot use. Understand first, then schedule.
• Survive being skipped. The intervals assume you show up. Miss two weeks and you are relearning, not reviewing.

That last one is the real failure mode. Almost nobody abandons spaced repetition because it stopped working. They abandon it because they stopped opening it.

Which is a product problem, not a memory problem - and it is the one Encodr is actually built around.