Cofounder conflict is one of the biggest untold stories of the startup world. Happens all the time, but no one wants to admit the scale of the problem or get into their own specifics.
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.
I too am glad my first cofounder flaked on me when I was just getting started. Learned a bitter lesson that I will never forget.
This is also why I went the solo route for #2 (ignoring the investor/"expert" insistence on multiple founders). 10+ years later my bootstrapped (non-tech) company is profitable, has a strong dedicated base of customers, and allows me a degree of flexibility in my company direction and life that I would not have otherwise.
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.