Seth Levine recently wrote a very nice post on humility that really made me think. For me, humility is inextricably tied up with perspective and expectation.
I have been fortunate enough to have had the opportunity to have many amazing experiences in my life already - and if I want to 'market' them, I can make it sound pretty sweet. But when you get a chance to do something cool, it's a good bet that you will get to meet some really impressive people along the way - and they can really help put things in perspective, keep you humble, and most valuably, raise your own internal expectations for yourself.
As an adolescent, I raced sailing dinghies a bit; I have become whatever I am (no name-calling!), Adam Koch, a guy I used to sail with, became a professional kite-boarder complete with videos, Red Bull sponsorship, 'signature' board, etc. Today Valleywag ran a quick bit about how people like Sergey Brin are hot for kiteboarding these days.
Since I work in an Internet startup - an end goal might be to start one (or several) companies of my own, and go big. That's a good goal - but I know that one day Sergey will be rigging up on the beach, turn to a friend and whisper: 'Dude, I think that might be Adam Koch!' Sure keeps me humble.
Here's a great video featuring Adam doing things like hucking off the deck of an aircraft carrier on his kiteboard: