Most people give up just when they're about to achieve success. They quit on the one yard line. They give up at the last minute of the game, one foot from a winning touch down.
~ Ross Perot
Ol' H. Ross was right on this one. So many times, people just sit down and give up when they could achieve their goals with just an iota more effort. It brings to mind those poor people one sometimes reads about--the ones who freeze to death a few yards from shelter. What causes them to plop down and say, "I'm not moving one more inch?"
I think it could be called a lack of vision. They can't see how close they are and so they assume the smartest course of action is to simply lay down and die. Or--even worse--they can see exactly how close they've come to their goals, but can't put one foot in front of the other even once more.
For most of us, though, it probably does boil down to an inability to see outside our own boxes and realize that with just one more degree of effort, our world could begin to change in ways too wild to imagine. There's a book about putting in that one extra degree of effort. It's called 212 by S.L.Parker. You can buy it from GiveMore Media. I highly recommend both the book, the philosophy, and Give More Media. They truly went the extra mile for me a while back when I bought the book as a gift for a client; I'm sure they'd be happy to help you, too.