The most common post YC failure case for the companies we fund, is they're incredibly focussed during YC on their company... and after they start doing a lot of other things. They advise companies, they go to conferences, whatever.

Press releases are easier to write than code, and that is still easier than making a great product.

You should be giving out a lot of equity to your employees.

Most founders have not managed people before, and they certainly haven't managed managers.

You need conviction in your own beliefs, and the willingness to ignore others naysaying.

If you compromise and hire someone mediocre you will always regret it.

Developing a personal connection with anyone you're trying to do a big deal with is really important.