I don't know that I can define it, I guess for me it is "knowing what I know", but the most enlightening book I have ever read is Dr. G. Michael Durst's (psychologist), Napkin Notes: On the Art of Living.

http://www.amazon.com/Napkin-Notes-M.../dp/0960255206

This book has to be read from the first page through, one can't skip around or one misses the thrust of the argument but from the first page it really pissed me off! I cannot tell you how many times I threw it But even today the things I learned and was forced to agree with (was unable to refute successfully so had to accept) help me out. Basically it is about accepting responsibility for one's self.

But, speaking of enlightenment, it starts with the story of a guru being sought by the protagonist and what the guru taught him.