Nobody gained anything and nobody really lost anything: the money was all theoretical so it never really existed. They owned x number of shares of a company which they could have sold for a certain price in 2021 if they wanted to. They would not be able to sell those shares at the same price now, so their "net worth" is lower. But it's all moot, nobody was really going to sell all those shares and it would be a nightmare to even try.

TL:DR - it's all stock market money which is made up anyways. Nobody ever had this money in their bank accounts.

You know how your headphones can reproduce any sound? Noise cancelling headphones have microphones to detect what outside sounds you're about to hear and then make the exact opposite sound at exactly the right time. Any sound (no matter how complex or loud) + its exact opposite = no sound at all, much like 5 + (-5) = 0.

I could get into superposition and all that, but that's probably beyond age 5.