"Product market fit is when your second employee is someone who's opening envelopes of money. eBay was such a good fit. Sellers were voluntarily sending in checks. Pierre had to hire someone, 'Hey, can you help me deal with all these checks that are coming in?'" Modest Proposal https://twitter.com/patrick_oshag/status/1312850056727457795

I remember meeting Bob Kagle at Benchmark in 1999 and talking to him about eBay. I don't recall anyone thinking that marketplaces would become as important a category as it would become. There were flops when a category didn't involve a hard buyer and seller coordination problem

After it's formation in 1999, Commerce One went from a $20B market cap to bankruptcy in a couple of years. Buyers and sellers bypassed it once they found each other and many already knew each other and found zero value. If you don't solve a real customer problem, you're dead.