Over a century ago, German psychologist Hermann Ebbinghaus put forward a theory on how quickly people forget information when no attempts are made to retrieve it. Here’s what the curve looks like:

Notice how quickly memory for information decays; most people’s brains forget information it doesn’t think it needs. This is why I’ve made the case that notes are incredibly important, an idea echoed by Curtis “50 Cent” Jackson as one of the most important lessons he learned from Robert Greene.

If you want to keep information, the brain is not always a reliable ally; it won’t remember what it forgot. 

Of course, deciding what to remember and preserve is also a skill in itself. Artful Prudence writes, “Samuel Coleridge classifies four kinds of readers; the hourglass, the sponge, the jelly bag, and the Golconda. The hourglass is immutable; it passes on what it absorbs. The sponge is like the hourglass, but a little dustier. The jelly bag is the most unintelligent, compressing all that is valuable and retaining the useless. The Golconda is possibly the most potent of all; it strains everything and holds on to the most precious jewels.” (I’ve also seen this attributed to Emerson.)

You don’t want to be an hourglass or a sponge; some people may start off as a jelly bag, and eventually get better at discerning between important information and useless information, developing the skillset of a Golconda.

One way to judge is to notice how many notes you’re taking from any given book. Robert Greene takes 20 to 30 notecards from a good book, and only 2 to 3 from a bad book. If you find you’re spending hours on retaining notes (and it eventually becomes a full-time job!), you may not be filtering out enough unimportant or irrelevant notes.

See strengthening brain connections, more on the forgetting curve, and the tyranny of the note taking industrial complex.