In YC experience, 2 or 3 co-founders seems to be about perfect.

One of the keys to focus, and why I said cofounders that aren't friends really struggle, is that you can't be focused without good communication.

... fire fast when it's not working. It's better for the company, it's also better for the employee.

Long term thinking is so rare anywhere, but especially in startups. This is a huge advantage if you do it.

The track record for founders that don't already know each other is really bad.

Before product/market fit, your only job that matters is to build a great product.

You have to find a small market in which you can get a monopoly and then quickly expand.