I'm a founder and I've gotten all lot of these. I usually don't take them to the heart, but at some point you start questioning yourself and they might shine a new perspective on it. They might be right, or they might be wrong, but the answer and the actions are mostly on you.

My take after all this is that you should question your friend, but if the drive is there, there's no point in arguing or being the "rational" one. The best way forward is support.