Literally, I could be responsible for an accident that totals a 15 year old car and gives the driver an ambulance ride and a couple day hospital stay and have my compulsory insurance not be enough to cover the entire liability.
Of course, nearly everyone carries a substantial (10-50x) multiple of the compulsory minimums in auto-specific liability policies, and if you have any amount of wealth accumulated, it's common to have an additional umbrella policy.
[0]-https://usinsuranceagents.com/massachusetts-car-insurance-re...
I guess the reason why US allows it is because the society is so litigious - if you have that amount of money to self insure you also have enough money to fight pretty much any claim against you.
Or one crash where you injure someone so bad that they cannot work anymore for the rest of their life, maybe need specialized support and so on. The damages in property are usually the least important part of a car crash.
https://slate.com/news-and-politics/2015/09/why-drivers-in-c...
Or injure a single person to an extent that requires lifelong fulltime medical care.