Person A see's a post about some crypto guy and how he paid off all his school loans with crypto, person A buys into crypto hoping for a similar outcome, this drives the price up. Person B seeing that the price has gone up regularly feels like he would be missing out if he didn't buy in, this drives the price up even more. Person A feels validated for investing because due to person B, the price has gone up, and maybe invests a little more, causing the price to shoot up, Person B feels validated... now imagine this circus with millions of people.