How I Met Your Mother, Season 6

Ted:
[addressing his architecture class] Unfinished. Gaudí to his credit never gave up on his dream, but that's not usually how it goes. It usually isn't a speeding bus that keeps the brown pointy church from getting built, most of the time it is too difficult or expensive, or too scary. It's only once you've stopped that you realize how hard it is to start again, so you force yourself not to want it. But it's always there and until you finish it always will be.