Fall in love with some activity, and do it! Nobody ever figures out what life is all about, and it doesn't matter. Explore the world. Nearly everything is really interesting if you go into it deeply enough. Work as hard and as much as you want to on the things you like to do the best. Don't think about what you want to be, but what you want to do. Keep up some kind of a minimum with other things so that society doesn't stop you from doing anything at all.
This quote from Richard Feynman is absolute gold. First of all, Feynman is the sort of intellectual you don't find in the world anymore. From Nobel Prize winning physicist, to naked bongo player on the roof of Caltech, to amateur artist, the sheer width and depth of his interests is astounding. It's the very opposite of what we see with so many intellectuals today -- a neurotic obsession with credentialism and playing it safe in a world where the personal and professional are intimately connected.
He also shows the value of having a LIFE outside of your speciality. His hobbies fueled his work and vice versa.
What I admire most about Feynman is his intellectual curiosity just for the sake of it.