I look at a YC investment (and most investments made by good angels) as less about the money and more about improving your chances of not dying. When you've got an early company, even if you're as far along as ColourLovers was, the biggest risk isn't that you will give up too much equity. The biggest risk is that you will die. And there are million reasons that you will die -- even for companies with great early traction. Things just happen.

But with backers like YC, you suddenly have a team of proven badasses that have a vested interest in making sure you succeed. So ask yourself, will YC _improve your chances of success_ by more than X%? If the answer is yes, take the deal. (Spoiler alert: the answer is yes.)