Here's our favorite by Historian David McCullough:
McCullough on hard work: “When the founders wrote about life, liberty, and the pursuit of happiness, they didn’t mean longer vacations and more comfortable hammocks. They meant the pursuit of learning. The love of learning. The pursuit of improvement and excellence. I keep telling students, ‘Find work you love. Don’t concern yourself overly about how much money is involved or whether you’re ever going to be famous.’ …In hard work is happiness.”
For more lessons on success from Maya Angelou, Sandra Day O'Connor, and more, go here.