People frequently ask how to find a cofounder. My first response is always that their cofounder should be someone they get along with and know well, like a friend. They usually respond by saying they've already tapped their friends and extended network, and everyone who's good is already doing something else, so they need to meet someone new.

This can work but assumes something that's almost certainly false. Namely, it assumes that it's easier to convince someone you don't know to join you than someone you do know. That would only be true if people like you less as they get to know you, which hopefully isn't the case.

You should assume the good people you don't know are much like the ones you do, and they all have other things they are or could be doing.

You'll need to convince them that throwing their lot in with you is better -- more profitable, more fun, more world-changing, whatever -- than doing something else. You're more likely to succeed at this if they already know you're a smart, hard-working and dependable person they respect and get along with.