Paul Graham - What You'll Wish You'd Known, written as a talk for a high school:
"Now I know a number of people who do great work, and it's the same with all of them. They have little discipline. They're all terrible procrastinators and find it almost impossible to make themselves do anything they're not interested in.
[...] The important thing is to get out there and do stuff. Instead of waiting to be taught, go out and learn.
[...] The only real difference between adults and high school kids is that adults realize they need to get things done, and high school kids don't. That realization hits most people around 23. But I'm letting you in on the secret early. So get to work. Maybe you can be the first generation whose greatest regret from high school isn't how much time you wasted."