It can get even worse than even that. If you trade other peoples money you can lose 9 times what they had in their accounts. And they will be on the hook for it.
One of the biggest in recent history have to be Einar Aas. An individual trader mostly trading electricity futures. https://www.nytimes.com/2019/05/03/business/central-counterparties-financial-meltdown.html
But you ARE already trading people's money when you trade with a 10 to 1 leverage: your broker's money, remember?