It comes down to herding. The 'normies' and trend chasers have come into crypto seeing 50%, 100%, 200% gains, and that's what they expect. When they see minimal / nothing / slight losses, they're reality model won't match expectations, and they'll pull their capital, but more importantly, pull their credit.
The main risk factor isn't that bitcoin goes down, it's that bitcoin stops going up.
Basically, most of the price increase in bitcoin, like any asset, is because of credit & leverage, not 'money' per se. People leverage to buy phat long stacks of BTC, price goes up, price increase covers the interest, no problems.
Problem is, price stops going up, maybe it just plateus for 3 months. So people stop buying on credit, they can't because they're tapped anyway, but not only that, then people begin to unwind their levered positions, this creates more supply, less sellers, price goes down, this drives more levered people out, price goes down more, everyone follows everyone, crash occurs. Also a crash isn't overnight, it happens over like a year.
Will this happen? No fucking idea. If shit with North Korea goes south, bitcoin will moon even fucking harder, if the hard fork is a 'thing', it will potentially deflate it, etc. Right now the risk to me seems more downside than upside, the odds of it doubling are lower than it halving, that's why I'm out for the moment.