Your goal should always be to have a successful startup. Even if you get into YC, it's no guarantee of success by far. The reason why YC wants co-founders is t

Your goal should always be to have a successful startup. Even if you get into YC, it's no guarantee of success by far. The reason why YC wants co-founders is that in the space of everyone that is a single founder, proportionally very little of them can actually do it alone. Compared to teams with two people. Being able to convince someone else to work with you on a crazy idea is a proxy that there's some merit to the idea.