Words of Wisdom from Sissela Bok

I am reading Exploring Happiness: From Aristotle to Brain Science by Sissela Bok, and early on I found these words:

"Yes, we are buffeted by forces and random events far beyond our control. But this is no reason to stop generating efforts of our own, to alter the situation in which we find ourselves...We become who we are in part by how we respond to the shifting circumstances against which our lives delineate themselves."

I'm interested these days in building fortitude, and determination, and so I latch onto quotes which reinforce my own efforts to work toward happiness. I'd be interested in knowing if you have mottos, phrases, or quotations that help you with your aims.