Nice idea, Adam. Let's try and keep this on the direct theme; it's a cool genre and there are other threads for more general quotes.
"Can you feel how empty and hollow your days are, how devoid of meaning? Have you forgotten what it’s like to really live a day that fulfills you deeply as a human being?" -- Mark Twight
"It is astonishing," says Dr. Theodore Cuyler, "how many men lack this power of 'holding on' until they reach the goal. They can make a sudden dash, but they lack grit. They are easily discouraged. They get on as long as everything goes smoothly, but when there is friction they lose heart. They depend on stronger personalities for their spirit and strength. They lack independence or originality. They only dare to do what others do. They do not step boldly from the crowd and act fearlessly." -- Orison Swett Marden, Iron Will
(this whole book is pretty much a collection of quotes like this, and much of Marden's other work is too) (and link is w/f/s, too)