I'm grateful that I experienced "cofounder mismatch" at a young age (23) and when the stakes were small. Basically, building an app with two friends when one wasn't committed at all, and the other was about half as committed as I was. Ended exactly how you'd expect (though thankfully, we're all still friends).

This is the chief reason why I'm the sole founder of my current venture. I'm not militant about avoiding cofounders (and I have actually scouted), but it would have to be a unicorn who is exceptionally good at the exact things that I'm bad at. Even then, I'd only do it after dipping my toe in over a number of months with smaller projects to gauge their personality and level of commitment.