Max Levchin described to me how this worked: Growth started to pick up after we gave $10 to every PayPal user who invited a friend, and also dropped $10 into the account of the person as soon as they signed up. The motivation to sign up was strong, but so was the motivation to continue inviting. People were already inviting each other, but this incentive supercharged viral growth. While it might have seemed like this would burn a lot of money, it increased engagement as well—we saw users send money back and forth within the network, and every time it happened, we recouped a little bit of the
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