Memory consolidation
Memory consolidation is how a fresh, shaky memory turns into a stable one your brain can keep. It happens quietly after you learn something, mostly while you sleep, when the brain replays what you studied and locks it in so it lasts.
Right after you learn something, the memory is fragile. A small distraction can wipe it. Consolidation is the slow fix. Over hours and days your brain strengthens the connections behind that memory until it sits still and stops slipping away.
Sleep does most of the heavy lifting. While you sleep, the brain replays what you took in that day and moves it from short-term storage into long-term storage. This is why pulling an all-nighter backfires. You can cram facts in, but without sleep they never get the chance to settle.
So the trick is simple. Study, then sleep. The studying plants the memory. The sleep makes it stay. Spacing your sessions over several days gives consolidation more nights to work, which is why a little each day beats one giant session.
Lena reviews her biology flashcards the night before bed instead of at 2am. She gets a full night's sleep. The next morning the terms come back faster, even ones she fumbled the evening before, because her brain locked them in while she slept.