Most of what you learn today will be gone within a day unless you review it

In the 1880s Hermann Ebbinghaus tested his own memory for nonsense syllables at intervals over days and plotted the results. Forgetting wasn't gradual and steady — it was steep at first, losing over half within an hour, then leveled off, a shape now called the forgetting curve. His related finding, the spacing effect, showed spaced-out review beats one long cram session.

— Hermann Ebbinghaus, Über das Gedächtnis (Memory: A Contribution to Experimental Psychology) — 1885
Go deeper: get the book →