At the end of the day, you really have to trust your cofounders. Betrayals happen but you can't found a company with people you don't trust.

A cliff still makes sense in cases when a cofounder abandons a start-up and stops working. Maybe the safest way for everyone involved is to only apply cliffs for the first 3 months or in the case of voluntary departure. That still leaves room for abuse but at least the temptation is more limited.

I'm sure the folks at YC have experience with just about every permutation of this scenario. I wish the video had also covered protecting the founders on the other side of a split up.