You'd be surprised at how hard it is for YC companies to get follow up investment, even with the YC stamp. I think YC tells that to their startups because they

You'd be surprised at how hard it is for YC companies to get follow up investment, even with the YC stamp. I think YC tells that to their startups because they believe it. YC has always been about elevating founders and making "start my own business" a viable alternative to "get a high paying job". And from day one their motto was "make something people want". And when you exit they give you a shirt that says, "I made something people want". They've always been product over everything else.