When you're on the outside looking at a team, it must seem as if the members share a purposeful determination. And they often do. But just as often, the startup effort simply becomes a new norm, inhabited by human personalities, inclined towards squabbling just like dorm roommates.
Membership in a startup team can amplify drama as much as suppress it. It fuels personal squabbles with a sense of import. The best way to resolve the overwhelming majority of conflicts is to walk away and let them cool down naturally. But in a startup, it's easy to tell yourself "we have to resolve this problem right now; the fate of the company is at stake!"
It's also probably the case that a lot of long-term simmering "important" issues actually started out as manageable problems that could have been dealt with, but for poor conflict handling early on; either the issue is broached and turns into a scalding fight, or fear of that fight keeps the team from addressing it early enough.
You would think this would mean founders with stable marriages would have an advantage. :)