What's the difference between active recall and passive review?

This is the most important finding in 100+ years of learning research. Passive review feels productive — you "feel like" you know it because the material is fresh — but the retention effect is tiny. Active recall feels harder because you're forcing the brain to retrieve, which is exactly why it works.

Flashcards are the easiest way to operationalize active recall at scale. Combined with spaced repetition, they turn a 30-minute daily habit into long-term mastery.