Without review, memories decay exponentially. Hermann Ebbinghaus showed that we forget ~50% within an hour, ~70% within 24 hours. But each well-timed review makes the memory stronger and slower to fade.
Cards start in Box 1 (review daily). Get it right โ it advances. Get it wrong โ back to Box 1. Each box has a longer interval, so you spend more time on what you struggle with.
All caught up. Come back tomorrow!