"Are you the co-founder who has clarity around the vision or are you the co-founder that's gonna build it?"
Failure mode: Both think they're in charge of vision, & then they constantly butt heads over what direction to go in.
One co-founder wants to make $100m from their startup, & another wants to be manage an Y person org.
Sometimes you can reconcile different goals, you just have to ensure they're not incompatible w/ each other long-term.
And then 6 months later, after you've blown up from all the built up resentment, you'll be in a room together wondering how you let it get so out of hand