It's minus half a credibility point for being a lone wolf founder. The reasons to have founders plural are countless.

As are the reasons to not have a cofounder. There is no pure formula for success.

Never said their was.

The wrong cofounder/s is like the wrong spouse.

The right cofounder/s is like the right spouse.

Best to know them previously, it helps a lot.

Further, the biggest point of having other people around is killing off bad ideas quickly because people won't see the entire picture themselves but they will believe their own bullshit. It's harder to delude yourself in the wrong direction of thought if your cofounder/s are there to help you keep you honest.