You don't have to read a whole book to learn from it and to think about it deeply. Sometimes, all it takes is two sentences, such as these two from Hosseini's AND THE MOUNTAINS ECHOED:
"I took solace only in hope. Hope that perhaps wherever she (the narrator's niece) is now, she has found as much peace, grace, love, and happiness as this world allows."
Peace, grace, love, and happiness. Four available but limited life gifts. Limited by a world that provides all of these, but in finite portions. The world won't "allow" any of us too much, which is both bad and good. Bad because we'll always want more. Good because if we got more, it would mean less.
And it's the only explanation for the next Hosseini truth I want to share.