Suppose Joe Investor bought a share of General Widget stock five years ago for $100 on the New York Stock Exchange. And suppose Joe Investor, five years later, decided he had overpaid. With the benefit of five years of hindsight, he now thinks the stock really wasn’t worth as much as he thought it was at the time. He overpaid. He feels kind of foolish. Imagine he showed up yesterday at the New York Stock Exchange and made his way past all the security to the exchange’s new chief executive, John Thain. And then imagine he said, “I’d like a very substantial part of my money back.”

Joe Investor would, to put it mildly, be told to get lost. He’d be laughed at. He’d be told that it just doesn’t work that way on Wall Street. If refunds were that easy to get on Wall Street, it’d be hard to count any sale or purchase as final — someone could always go back and name a new price at which to redo the transaction.

So it was nothing short of astounding to read in yesterday’s papers that Mr. Thain is attempting to make this sort of move on the New York Stock Exchange’s former chairman, Richard Grasso. The stock exchange’s board bought Mr. Grasso’s services on the open market, just the way Joe Investor buys stock in General Widget. The stock exchange board paid him $140 million. Now, just like Joe Investor, it feels foolish for having overpaid. And in real life — not some hypothetical scenario — Mr. Thain says he wants some “very substantial” part of Mr. Grasso’s pay returned.

It’s not as if the stock exchange’s board were some group of naïve grandmothers who overpaid for General Widget stock because they got the hard sell from an overly enthusiastic stockbroker. That board that was paying Mr. Grasso included some of the sharpest executives on Wall Street, high-powered lawyers, experienced public servants. It even included the chief executive of Goldman Sachs, Henry Paulson Jr. If Mr. Thain thinks Mr. Grasso was overpaid, maybe Mr. Thain — a former Goldman Sachs president — should go after Mr. Paulson’s back salary for allowing the payment of Mr. Grasso to go forward. Once you start opening up these transactions and trying to re-adjust them after they’ve taken place, there’s no end to it. The next thing you know, investors will be lining up at the stock exchange asking for partial refunds on stock they belatedly realize they overpaid for. It’s no way to run what’s supposed to be the premier institution of capitalism.