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.

>>20
i just find it a mixture of funny, saddening, and irritating that in a world where people have extremely little time to read they tend not to reread things they've read. because they don't have time to or simply don't want to waste what little time they have rereading something as opposed to reading something new.