Two wonderful quotes from W.H. Auden's book The Dyer's Hand:

Between the ages of 20 and 40 we are engaged in the process of discovering who we are, which involves learning the difference between accidental limitations which it is our duty to outgrow and the necessary limitations of our nature beyond which we cannot trespass with impunity.

And this, which I love:

Pleasure is by no means an infallible critical guide, but it is the least fallible.