[jacquesm]

I'm not sure what rule the OP is referencing but otherwise reasonably successful start-ups often fail because founders clash on key parts of their vision (or behave in toxic ways towards each other or to other people in the company). This can very handily wreck your company or at a minimum substantially damage it.

[j45]

Rule was a typo, I meant observation.

Specifically, cofounder strife is one of the major issues of startups that don’t get where they could.

If I recall it was Jessica Livingstone’s observation

[jacquesm]

Rule or observation doesn't matter all that much (it's a shade, after all) and the whole idea lines up with my personal experience.