system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are billionaires able to pay such a low tax rate?

I know they write off stocks somehow, and some use something called the "variable prepaid forward contract" however this stuff makes my head spin.  Can anyone break down how this is possible?
gpt
Billionaires make most of their money off various sorts of investment income (which affects a very small percentage of the population) rather than payroll taxes (which affect most people).

Given the total tax liability of a typical billionaire, it's usually very cost-effective to do some combination of restructuring their income to avoid taxes (relatively easy, since they're probably a CEO or major shareholder of a company that employs lots of high-level accountants), or lobby the relevant national government to add a few tax loopholes that benefit billionaires with their specific income structure. 

In other words, you don't need to understand the details of the "variable prepaid forward contract;" the important thing to understand is that once you make a sufficiently insane amount of money, it's much cheaper to game the tax system than to pay your fair share.