You want to fail as quickly as possible. Startups are like dating. If its not going to work out you want it to bomb quickly, so you don't waste your time and so you can move on to the next one...
A bunch of us got that out of the way!
A friend of mine is a marathon runner who usually comes in under 3 hours. It turns out that there are enough people in that category that the Boston Marathon offers slots by lottery, and this year he wasn't one of them. Not getting a slot in the Boston Marathon doesn't mean you can't finish the race; it just means you have to find a different place to run.