The founder of a successful company is typically "rich" in the sense that he owns a large number of shares of stock that are worth a lot of money. But you can't eat stock. If you want to turn your riches into crazy parties on your superyacht you need money. You could get the money by selling your shares, but there are two problems with this. One, it would dilute your control over the company. Two, it might be taken as a signal that you lack confidence in your own firm. So what's a founder to do?
One strategy is to borrow money. You may think of borrowing as something people do when they're poor, but it's actually a very appealing strategy for certain classes of rich people. You can post your stock as collateral on loans, use the loans to fuel consumption, and as long as lenders have confidence in the underlying value of your shares you can roll debts over and keep the party going. This is basically the founder's version of taking out a home equity loan against the value of your house, as many Americans did in the aughts when they found the book value of their homes suddenly rising. But just like Mr. and Mrs. HELOC, your founder can end up in trouble if the value of the underlying assets starts to drop.
Hence the sad story of Robert P. Stiller, founder and chairman of Green Mountain Coffee Roasters, maker of those Kuerig machines and the little green single-serve coffee pods that fuel them. He wound up needing to sell a bunch of the shares he'd posted as collateral after short-sellers began undermining confidence in the firm. The large-scale sale further eroded confidence in the firm, violated the company's internal trading policies to boot. Now Stiller's been removed as chairman of the board, booted unceremoniously from his own company.