Non-fiction books you read more than once.

If somebody is willing to read a particular non-fiction book twice or more, then it’s at least worth checking out.  And that helps sift the wheat from the chaff in a plethora of books that could be a potentially HUGE waste of time. I must find more diamonds in the rough.  

Also, if you could also explain why, it would help me (and others) understand the appeal that motivates you to read it more than once.

The Tao of Writing by Ralph Wahlstrom was a good read, and helpful.  Does anyone know of any similar books that could get someone who draws/paints out of a creative block?