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.

>>23

I don't think that's what he or she was saying. You do not have to read every book you've bothered to read once, again and again. However, there is a lot of learning and understanding being lost because most people never give good books that second time around. They should re-read if only to see how their understanding of a book has changed with their newer, more 'up-to-date', mind.