^ What everyone else said; I especially feel good about myself when the higher-ups at work notice that I've done something well. Not because I'm trying to suck up (because I'm not), but when they notice I've not done it FOR THEM, but FOR ME and STILL think highly of me.
... or when (and this is a true story) I first started taking Econ. in school - the first three or four weeks were a nightmare; I didn't understand it at all, and I was fearful of flunking the course. Then it suddenly clicked, and I was like ... WOW, I LOVE THIS CLASS. And then on top of all the trials I had to deal with up to that point ... I ended up with the highest grade in the class at the end of the semester. I love the subject matter now and to this day like discussing it with other people that are willing to have an intelligent conversation about it.
Lastly, diagnosing what's wrong with my car. I don't ALWAYS know what's wrong with it, but I've had it long enough that I usually get it right about 80% of the time. Saves a lot of time, trouble, and money.