Hunter S. Thompson, an American journalist, wrote this letter in response to his friend's request for life advice.
Thompson had an unorthodox daily routine of waking at 3pm and filling his hours with whiskey, coffee, cigarettes, and cocaine.
I acknowledge the irony here, for presenting someone whose life was sustained by stimulants and depressants. Yet I do find his advice on finding life's purpose quite illuminary. Here are my favorite quotes:
A man must choose a path which will let his ABILITIES function at maximum efficiency toward the gratification of his DESIRES.
In doing this, he is fulfilling a need (giving himself identity by functioning in a set pattern toward a set goal), he avoids frustrating his potential (choosing a path which puts no limit on his self-development), and he avoids the terror of seeing his goal wilt or lose its charm as he draws closer to it (rather than bending himself to meet the demands of that which he seeks, he has bent his goal to conform to his own abilities and desires).
Decide how you want to live and then see what you can do to make a living WITHIN that way of life.