Paul Graham, a venture capitalist from Y Combinator, has put up a speech that he gave at one of their dinners. You should all read this, it is certainly worth while, especially for startup businesses.

When startups die, the official cause of death is always either running out of money or a critical founder bailing. Often the two occur simultaneously. But I think the underlying cause is usually that they've become demoralized. You rarely hear of a startup that's working around the clock doing deals and pumping out new features, and dies because they can't pay their bills and their ISP unplugs their server.

Startups rarely die in mid keystroke. So keep typing!

If so many startups get demoralized and fail when merely by hanging on they could get rich, you have to assume that running a startup can be demoralizing. That is certainly true. I've been there, and that's why I've never done another startup. The low points in a startup are just unbelievably low. I bet even Google had moments where things seemed hopeless.

Read the full speech
There are some other quotes from the essay which I think are worth sharing,

...startups run on morale.
Distraction is fatal to startups.