In times of crisis, unless you were early, you may find that you cannot do anything with your stocks, they are frozen and then they go down with the ship.

If we're not thinking systemic crisis, then the stock can just become next to worthless before you can get it sold.

Here's a crazy story: Celcius was a crypto exchange that had in its terms that your crypto was your crypto. Then they started to go bankrupt and a lot of people withdrew (bank run) and then it froze. Many could not withdraw. The courts ruled that the crypto belonged to Celcius and that it should be used to pay investors before customers.

If it stopped there, that would be a complete story, but then they recently started suing anyone who withdrew a few months before they could freeze assets... people who took their funds into self custody are being sued so that the company can claw back more of their customer's money after the customers felt like they got out safe. These customers did nothing wrong. Banks and trading platforms can behave the same. They just have insurances and other systemic assurances that stop them from doing such drastic things... in many cases, that stop them from going bankrupt. Those assurances are not free, it steals from the poor (and maybe a bit from your left hand) because it fuels inflation.