[edited] I wonder if humility and thankfulness might help.

Not humility in the sense that you put yourself down, but humility in the sense that you accept that you're part of a large world (and a huge universe) and that you're happy with that.

And being thankful for the things you've been able to achieve, the help you've received along the way etc.

You can quite easily practice both. http://www.google.com/search?q=practice+thankfulness