US tax laws are monstrously complicated. There’s a couple thousand pages of tax code, along with close to 10,000 pages of IRS regulations, that you won’t understand adequately unless you’ve also studied the many tens of thousands of pages of related case law. There is no single person alive who fully understands US tax laws, and even a well resourced team of people likely won’t when combined.

It’s possible to understand it well enough to get by, but you’re pretty much guaranteed to make mistakes in one way or another, and some of those mistakes are pretty much guaranteed to be criminal offences. You could live your whole life without that ever becoming an issue, but the gamble you’re taking isn’t that you’re never going to make a mistake (you will), it’s that the IRS will never commit any considerable resources to investigating your mistakes.