Sometimes, for me at least, just reading books is not enough to understand a concept. That is why we have exercises in text book to test and get used to new concepts. But, for me, writing about what I've just read is another way that helps me to understand. Can you say "exorcising" things too much difficult to understand on the first reading pass ?
This is why I maintain a web site called MyDevNotes.
Take a look at it... maybe you'll learn something just... by reading it!