[1] https://www.pbs.org/newshour/economy/making-sense/the-income...
I can explain it to you with a simple example:
Imagine, for instance, you're making 50k a year and have a brokerage account that has appreciated by 100k and that you're being taxed 20% on unrealized gains in year x. In year x+1, say your account falls back to where it was before. You paid 20k plus another 10k, and you will need to set aside another 10k. In essence, your income has been reduced to 10k, which could make daily life impossible for many people making 50k annually, especially those with families.