[solve]

(Most) accelerators are the problem here. They stack all the incentives on adding a cofounder no matter what, and none of those that I've closely known would stand behind the idea of "A bad cofounder is far, far worse than no cofounder." E.g. if your original cofounder leaves, they'll lay big penalties on you if you don't refill that seat immediately, even if it's bad for the company.

What investors tend to leave out here is a real incentive for them, as a class. It's far easier to fire a founder if there's two. If there's two, it's often easy to make them turn on each other if they want one forced out. Forcing one of 2 out tends to be much less frowned upon, than kicking out the sole founding CEO and replacing him with outside management. Having 2 cofounders is big leverage for keeping the founders in line.