I just came across an interesting analysis about Jeff Bezos’ net worth, and it made me think of a fact that many people easily overlook: one of the richest people in the world may actually have far less money he can truly take out and spend than you might imagine.

Bezos’ current net worth is about $235.1 billion, which sounds astronomical. But here’s the key issue—most of this money is not sitting in bank accounts as cash. His wealth is largely tied up in Amazon stock, accounting for more than 90% of his total assets. This brings us to an economically important concept: liquidity.

Simply put, liquid assets are things that can be quickly converted into cash—stocks, bonds, cash, and the like. Real estate, artwork, and private businesses are non-liquid assets; when they’re sold, it takes time and they’re also prone to losing value. Typically, most high-net-worth individuals keep only 15% of their assets as cash or cash equivalents, but Bezos’ situation is special. His 9% stake in Amazon is valued at about $212.4 billion, which, in theory, looks highly liquid.

But then an interesting paradox comes into play. If the largest part of Jeff Bezos’ net worth—the $212.4 billion worth of Amazon stock—were really to be sold off in full, the market would crash outright. If a founder suddenly dumps that many shares, it would trigger panic selling, the stock price would plunge, and in the end the money he could actually walk away with might be only a small fraction of its book value. It’s like holding a super valuable coupon—until everyone in the world tries to use it, and then the coupon is effectively worthless.

In addition to Amazon stock, Bezos has an approximately $0.5 to $0.7 billion real estate investment portfolio, and he owns two private businesses: The Washington Post and Blue Origin. Taken together, these assets are indeed substantial, but again, none of them are assets that can be converted into cash quickly. So even if Jeff Bezos’ net worth is very high, the amount of liquid funds he could truly pull together for a big transaction today is, relative to his total assets, still a relatively small figure.

This case actually reflects a bigger truth about wealth: book net worth and real purchasing power are two different things. For super-rich people like Bezos, the core issue isn’t how much money they have—it’s how liquid that money is.