Hey, you may not be ready to take investor money and that's completely fine. Maybe you've realized you'd rather have a bootstrapped business instead of a unicorn. Cool, actually think about what taking investor money means. Figure out what's best for you and your team.
To be fair, this letter was targeted at companies in the current YC batch. They've already explicitly opted-in to going the venture route, at least in some capacity.
Bootstrapped businesses can be awesome; I've built a couple myself. But the time to be asking these sorts of existential questions would be before you take VC money, not after.
For a group that focuses primarily on young, inexperienced founders and is so founder focused, I think it would be reasonable to expect them to allow for founders to take the exit ramp if they decided the VC route didn't make sense for their business based on their YC experience.
Hey, you may not be ready to take investor money and that's completely fine. Maybe you've realized you'd rather have a bootstrapped business instead of a unicorn. Cool, actually think about what taking investor money means. Figure out what's best for you and your team.