And guess what those business have? Valuations. Stock price is just an aggregate indicator of the valuation for a company, for the given percentage of shares that are publicly traded. But private companies have valuations, too, and even if they’re not tied to a public stock offering, those valuations are used to form these Billionaire lists.

Same thing with real estate. The value of any asset is based on what someone is willing to pay. Sometimes, you’ll find some crazy billionaire or investment firm who grossly overvalues an asset relative to their peers, and that insane overvaluation does get rolled into those lists.

But such is the nature of economics. You’ve neither gained nor lost value until someone pays you. Until then, it’s anyone’s guess.