Obviously, it's good to strive for creativity and novelty in your work, but you also have to maintain a sense of perspective: if you've set your goals so high that your definition of "achievement" is isomorphic to "originality", then you're probably in for a lifetime of disappointment. It's a hard problem to be original -- there are a lot of other people in the world, and most of them are trying to be original, too. In fact, being original is a lot like being famous, because you can strive for it, but your success is largely determined by what other people do; it's probably bad to condition your self-esteem on the actions of other people.
For what it's worth, here's my half-formed philosophy: you have to do whatever it is that gives you a sense of personal satisfaction and contentment. Your accomplishments don't have to be great; they don't have to be original; they don't have to make you famous. As long as you can look in the mirror in the morning and feel excitement about the day, you're doing pretty well.
Perhaps I should have described another trap. It is too easy to grow up with the sense that one should work on only grand things.
"The worthwhile problems are the ones you can really solve or help solve, the ones you can really contribute something to. [...] No problem is too small or too trivial if we can really do something about it."