people withdraw into conservative assets (relative to what they have their future outgoing cashflows, ie. if they have to pay for food in dollars, they'll hold

people withdraw into conservative assets (relative to what they have their future outgoing cashflows, ie. if they have to pay for food in dollars, they'll hold dollars to minimize risk of exchange rate shifts) and to cause a dam burst it's enough for a trickle of retail investors to start doing this. and .. bam. you saw the last few weeks. (as others notice that there's less and less chance of making money they also withdraw to minimize risk)