I've been trying to get many people around me to read this book, The Dip: A Little Book That Teaches You When to Quit (and When to Stick) by Seth Godin:
http://www.squidoo.com/theDipBook/
It's expensive for how extremely short it is, but the one idea it contains is so powerful and important that it's well worth it. Basically the idea is that when you start some new thing, there's a period of exciting growth and reward, but then eventually it becomes an unrewarding slog (the dip). But if you pour enough energy into something for long enough, eventually you climb up the other side of the dip, and things get super awesome. That sometimes takes a ridiculous amount of energy, which means quitting a bunch of other things that are consuming your time and energy but where you're not determined to get out of the dip.
Having this idea in my head has changed the way I see so many things, and is already affecting the way I live my life. Most of all I want to stop the pattern I've had of starting things and then getting fed up when they start to require a massive investment just to make a tiny bit of progress - and then feeling resentful when I see the people who did put in that investment rather than quitting, and made it to other side of the dip where their life looks awesome. I'm going to start to value that period of grind for some small number of things, and for the rest quit them intentionally and cheerfully.
Here's a good companion piece to the book, with some additional handy terminology:
http://ihack.us/2007/05/25/dips-dead-ends-lotteries-and-quests/
