You forget most of a lecture before dinner
The nineteenth-century scientist who first mapped how fast memory decays also discovered the cheap trick that beats it.
In the 1880s, Hermann Ebbinghaus ran a strange experiment on the only subject he trusted completely: himself. He memorized lists of meaningless syllables, then tested his own recall at intervals from twenty minutes to weeks later, tracking exactly how much slipped away and when.
The curve he plotted was steep and unforgiving. Most of what you learn vanishes within the first day, and it vanishes fastest right at the start — memory doesn't erode evenly, it collapses early and then levels off. Modern replications, run well over a century later, have reproduced his original shape almost exactly.
But Ebbinghaus also found the one variable that changes the curve's steepness: spacing. Study something once, then let time pass, then deliberately try to recall it before you've fully lost it, and each retrieval flattens the future decline. Cram the same material all at once and you learn it faster today at the cost of losing it faster tomorrow.
The forgetting isn't really the problem. Scheduling around it is the whole trick.