If someone is choosing between joining McKinsey or your startup it's very unlikely they're going to work out at the startup.

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

Ideas by themselves are not worth anything, only executing well is what creates value.

You want an idea that turns into a monopoly. But you can't get a monopoly, in a big market right away; too much competition for that.

Later, you should learn to hire fast and scale up the company, but in the early days the goal should be not to hire. Not to hire.

One of the great and terrible things about starting a start up is that you get no credit for trying.

By the way, that's my number one piece of advice if you're going to join a startup: pick a rocket ship.