Check out this great post from Union Square Ventures:
My friend Dick Costolo, co-founder of FeedBurner, describes a startup as the process of going down lots of dark alleys only to find that they are dead ends. Dick describes the art of a successful deal as figuring out they are dead ends quickly and trying another and another until you find the one paved with gold.
This relates to my Fundamental Theory of Startups: success is about staying in business long enough to get to the third idea.