[imjk]

Read the "Founders at Work" chapter on Max Levchin and Paypal. In PayPal's early stages, there were multiple companies all trying to do online money transfers securely. They were all fighting fraud to the tune of millions of dollars daily. Eventually, PayPal was the first to figure out some ingenious ways to combat fraud. With the first reliable online money transfer network, they were able to dominate the market, especially on Ebay then the largest ecommerce site. tl;dr - Winner-take-all market.