Updated: Jan 27, 2018
When I read a book, I like to underline and write down the page number of what I underlined on the inside cover. The purpose of this is because when I go back to a book years down the line I don't want to read the whole book to remember what I already read. It's kind of like watching an old movie but the opportunity cost of re-watching an old movie isn't nearly as high as having to re-read a whole book again.
There are loads of information and knowledge in a book, but certain parts will stand out to me much more than it may stand out to you based on our different experiences, interests, and personalities. I just finished reading Ideas And Opinions by Albert Einstein a couple of days ago. I read this book because I believe that Einstein is the smartest man ever. Warren Buffett has said that if he could meet anyone to have ever lived, he would want to meet Isaac Newton because he thinks that he was the smartest man. He certainly has a case, but I happen to think it's Einstein and that is why I started reading this book.