In addition to relentlessly resourceful, you want a tough and a calm cofounder.

It takes years and years, usually a decade, to create a great startup.

For most software startups, this translates to keep growing. For hardware startups, it translates to don't let your ship date slip.

You also want to fire people who a) create office politics, and b) who are persistently negative.

Most of the best hires that I've made in my entire life have never done that thing before.

You really want to know your cofounders for a while, ideally years.

The other piece besides focus for execution is intensity. Startups only work at a fairly intense level.