you are not understanding. What he means is someones' assets can show he is a billionaire, yet in actuality it is all on paper. He has no cash available unless he were to convert, as an example, stocks into cash by selling them. And depending on the market he could end up with much less than the worth it had been declared. Just one of many examples.
Can you imagine those billionaires that have most of their worth in stocks, commodities, etc. suddenly having to sell them all and what would then happen to the economy?
I think you exaggerate how much disposable money a billionaire has access to.
Here are some examples for you of those that have lost much of their worth-
Thomas Friedman of the New York Times went from $3.6 billion to less than $25 million in a matter of a year.
In 2001 BET founder sold his company to Viacom for $4 billion, yet because of a nasty divorce, bad real estate deals, and the loss of value in Viacom stock lost all but $550 million in one year.
In 2008 Mark Zuckerburg lost $900 million of his worth of $1.5 billion.
In 2007 Randal Nardone was worth over $10.7 billion through his hedgefund. He lost 91% of that value in one year.
What many people do not realize is that most peoples net worth is all tied up in paper assets. Say I purcahse a home that is worth $250,000 and take a loan out for that amount. I have another $10 grand in savings. My net worth is now $260,000 even though I just took out the loan on that home and I still owe all but my down payment on it. That is just an example of net worth for you. Do I actually have access to $260,000? No. And if the real estate market crashes, then my net worth drops even more, even though I am still responsible for paying for a $250,000 mortgage. And what happens if I need to sell? Then I am still obligated to the bank for that $250,000 even if I can only sell the home for $190,000. I have derived an added debt of $60,000 on something I don't even own anymore.
Net worth that you hear about of individuals is the total of their homes, real estate holdings, vehicles, stocks, treasury bills, etc. and of course any cash they may have accumulated, retirement funds, etc. Even though they may owe the banks for most of that, it is still considered their net worth. If they suddenly were to lose most of all of the above, through poor investing, economies, etc. and they had to turn to their retirement savings, and had to withdraw from them early just to live, even then they would be worth much less than that fund shows on paper as there are penalties for early withdrawal. Even money in the form of cd's, money markets, etc. can be subject to early withdrawl penalties.