This comment is full of so many absolutely true statements, I love it.

If you live in the US you are expected to declare income to the IRS regardless where you earned it. If you reside in WI and earned money at a job performed in FL, you have to declare it on the WI state form (even though FL is state-tax free). If you earn money through a job, capital gains, a deceased relative, excessive gambling earnings, and even working a side-job for cash you are supposed to declare it and pay taxes to enjoy the programs offered by your country.

Obviously there are many situations where there is a "you don't report, I don't report" agreement...nobody wants to pay taxes if it can be kept. But theoretically you can report paying a housekeeper cash, and they can get in trouble if they don't report it, too.

It's just called tax evasion. Being a successful daytrader or currency exchanger doesn't give a hall pass. Eventually the government will audit purchase patterns and question where your money came from. If it came from unreported capital gains from the crypto market you'll have to pay back-tax, go through repo, and possibly serve jail-time.