"The greatest use of a life is to spend it on something that will outlast it."

Practically speaking, there’s no purpose to doing something that outlasts you. You won’t be there to see it anyway. But that’s not the point. If we live our lives every day with that idea in mind—that we should strive for doing/creating useful things that matter to others—we end up spending our time on things that actually make a difference. When you do that, life automatically has meaning—to everyone.

Source: THINK STRAIGHT: Change Your Thoughts, Change Your Life by Darius Foroux