Okay, here's one I just made up, but it's so far-fetched nobody would ever believe it.

WHY THERE ARE NO GIANTS TODAY
Back in the days when giants walked on Wall Street, a particularly greedy giant came up with a new idea for how to make money from next to nothing. His idea was that he would loan money for home mortgages to anyone who wanted it, regardless the borrower's ability to pay it back. The payments would start out cheap and then suddenly inflate to something the mortgagee wouldn't be able to afford. Then the giant would foreclose on the propery and resell it at a profit. After all, real estate prices had been increasing for as long as anyone could rememember.

The scheme worked pretty well as long as there were just a few giants in on it, but the day came when so many giants were playing the game that real estate prices started to fall. It turned out that even giants weren't immune to the laws of supply and demand. When that happened, the giants weren't able to sell their foreclosed properties at all, much less at a profit. Poor giants.

It would be a sad enough tale if it had ended there, but it didn't. You see, the money the giants had loaned in the mortgage game hadn't really belonged to them. They had borrowed it from even bigger giants. And since there was no money coming in on the foreclosed properties, they weren't able to make their loan payments to the even bigger giants. And guess what! The even bigger giants didn't really "own" the money either! They had borrowed it from humongous giants. And the humongous giants had borrowed it from the really huge monstrous giants, who had borrowed it from.... You get the picture? Nobody was able to repay the money they'd borrowed and, ultimately, the whole giant society collapsed into a heap. And that's why there aren't any giants around today.