But how had I come to believe in this idea in the first place? A
combination of my own experience and other things I'd read.
None of which I could at that moment remember! And eventually
I'd forget that Hilbert had confirmed it too. But my increased
belief in the importance of this idea would remain something I'd
learned from this book, even after I'd forgotten I'd learned it.
Reading and experience train your model of the world. And even
if you forget the experience or what you read, its effect on your
model of the world persists. Your mind is like a compiled program
you've lost the source of. It works, but you don't know why.
The place to look for what I learned from Villehardouin's chronicle
is not what I remember from it, but my mental models of the
crusades, Venice, medieval culture, siege warfare, and so on.
Which doesn't mean I couldn't have read more attentively, but at
least the harvest of reading is not so miserably small as it might
seem.
This is one of those things that seem obvious in retrospect. But it
was a Surprise to me and presumably would be to anyone else
who felt uneasy about (apparently) forgetting so much they'd
read.
Realizing it does more than make you feel a little better about
forgetting, though. There are specific implications.
For example, reading and experience are usually "compiled" at
the time they happen, using the state of your brain at that time.
The same book would get compiled differently at different points
in your life. Which means it is very much worth reading important
books multiple times. I always used to feel some misgivings
about rereading books. I unconsciously lumped reading together
with work like carpentry, where having to do something again is a
sign you did it wrong the first time. Whereas now the phrase
"already read" seems almost ill-formed.
[1] P. Graham. How you know. Dec 2014.
https://www.paulgraham.com/know.html