Extensive reading vs Intensive reading

There are two ways to read one is extensively which is reading as many book as possible as quick as possible and intensive which means reading slowly and fewer books but with more focus on the actual contents of the book. The problem with extensive reading is that it gives us less time to digest the material in each book. A few months ago I read a book, and all I can tell you now is that it was good and had a rather clever gimmick for envelopes in it. That's all I remember, can't even remember what the gimmick is. I'll never be a good magician just from read as many books as possible. I need to really take in what I'm reading. To that end I'm going to start writing stuff down as a read, and force my self to pay attention and re-read  parts that are important.