You don't have to read a whole book to learn from it and think about it deeply. Sometimes, all it takes is four sentences, such as these from Hosseini's AND THE MOUNTAINS ECHOED:
(The narrator, this time, is Pari, now an older woman sharing some of what she has learned about life with her namesake niece.)
"I should have been more kind. That is something a person will never regret. You will never say to yourself when you are old, 'Ah, I wish I was not good to that person.' You will never think that."