After reading a lot about the startups at YC, I was a bit baffled to see that most people only talk about the exit strategy.. Doesn't anyone care about building a sustaining business anymore, or is this just part of the YC agreement ?
IMHO, people start on businesses with the assumption that it is going to be a success. But that assumption turns out to be true only a very few times. When there is such a high chance of failure its just smart that you also make plans for such a negative possibility.
An exit strategy is to ensure that when you give your idea a try, you should still come out unscathed if it doesn't work out and if possible be still make some money to try out your next idea.
It is just like insurance, you don't buy it because you want somethig bad to happen (well.. in most cases :)), but in case it happens.
If you are a programmer, this may make more sense - there is a reason you have 'if... else..." and not just 'if'