Affirm CEO Max Levchin on why PayPal produced so many founders: "As we were interviewing certainly the early team and even the later team, we kept on selecting for entrepreneurs. One of the stock questions I would ask was, 'So what are you going to do after PayPal?'" "The answer that I welcomed the most was, 'Oh, this is the last one. I'm going to start my own afterwards.' If you're coming in here to get your final graduate degree in entrepreneurship, of course we'd love to have…