Who Shapes the Clay of a Man's Life?

There are so many good quotes from The Walking Drum, by Louis L'Amour, but I just had to share one that I would love to tell many people I have encountered in my life:

Up to a point a man's life is shaped by environment, heredity, and movements and changes in the world about him.
Then there comes a time when it lies within his grasp to shape the clay of his life into the sort of thing he wished to be.
Only the weak blame parents, their race, their times, lack of good fortune, or the quirks of fate. Everyone has it within his power to say, this I am today, that I shall be tomorrow. The wish, however, must be implemented by deeds.