The best moment to review something is the last moment before you would have lost it. Review too early and you waste the effort. Review too late and there is nothing left to save.
This runs against instinct. It feels responsible to go over new material while it is still fresh, while you can still recall it easily. But easy recall does almost nothing. If the answer comes without effort, the memory was never under any strain, and strain is what strengthens it. The small struggle to pull something back from the edge of forgetting is the entire mechanism. No struggle, no gain.
So the ideal review sits right at that edge: late enough that retrieving the answer takes real effort, early enough that you can still retrieve it at all.
And the edge keeps moving. Each time you recall something successfully, it sticks for longer, so the next review can wait further out. A fact you needed to see again tomorrow might hold for a week after one good recall, then a month, then longer. The intervals stretch as the memory hardens.
That is also why doing this by hand falls apart. Tracking the moving edge for one fact is easy. Tracking it for a few hundred, each on its own schedule, is impossible to hold in your head.
That edge is exactly what Cucaracha tracks for every card, so you can stop guessing about timing and just show up when there is something to review.
Knowledge that never dies.
Cucaracha builds the cards and brings each one back the moment before you’d forget it. You just show up.