...but that's exactly what OP said, no?
I remember attending an ML presentation where the speaker shared a quote I can't find anymore (speaking of memory and generalization :)), which said something like: "To learn is to forget"
If we memorized everything perfectly, we would not learn anything: instead of remembering the concept of a "chair", you would remember thousands of separate instances of things you've seen that have a certain combination of colors and shapes etc
It's the fact that we forget certain details (small differences between all these chairs) that makes us learn what a "chair" is.
Likewise, if you remembered every single word in a book, you would not understand its meaning; understanding its meaning = being able to "summarize" (compress) this long list of words into something more essential: storyline, characters, feelings, etc.