I feel like if I need to re-read a book to better understand it, either I or the book sucks. It doesn't seem very efficient.
Depends on the book, of course, but usually yes. Especially with books that deal with complex subjects such as mathematics and human interaction.
I remember re-reading (and re-writing) the whole Analysis textbook in college - the second pass through it gave me much more intuitive understanding of it. The third made me love analysis.
I also remember the book How To Win Friends And Influence People which explicitly recommends re-reading the book every now and then, allegedly to make us internalize the writing better.
The two most important points were:
1. Anything could happen 2. We can only control risk
While these points were related to trading, I slowly started to apply to pretty much everything.
I used to think, like code, I can perfectly control outcome of any serious effort. Now I know in real life, you can do everything perfect but still get unexpected outcome.
It sort of prepare me for unexpected and always think about backup plans.
But books themselves dont create nothing. People do. Either themselves or typically by influences of other people.