Small-ish startups seem to be able to do about three things at once, and usually they are whatever the CEO is focusing on. Anything that is not someone's number one or two priority is unlikely to get done in the hectic world of a startup.

Most founders know what to do; they just don't know what not to do. It's very easy to justify taking on one more project by saying it won't be that time consuming—but it will either be time consuming, or it won't be worth anything.

The Y Combinator version of focus is 'write code and talk to users.' Worrying about corporate structures, interviewing lawyers, doing bookkeeping really well—all of this pretending-to-run-a-company gets in the way of actually running a company.

Hiring well is the highest-impact thing a founder can do for his startup, and the best thing an investor can do is fund great founders. 'Always be recruiting and promoting talented people' is very good advice.

Working with your friends is a good strategy—smart, effective people tend to like other smart, effective people. The best hires Altman has made or seen others make are usually friends or friends of friends.

Spending time on personal relationships seems to conflict with focus, but it's an important exception—and one of the most enjoyable parts of work.