These are heady and concerning days for those of us who follow financial markets. Irrational exuberance is everywhere. Stocks are trading at or near their all-time highs and bonds are moving upwards in defiance of anything that resembles common sense. As a journalist and former longtime M&A banker, I have always enjoyed rolling calls—I dial myself of course—with some of the keenest minds in the financial industry, often to jawbone about the absurdity that occasionally overtakes the peculiar business of making money from money. More recently, however, my conversations with Wall Street executives and leading economic thinkers have turned to the darker, inevitable question of what happens when the music stops, as it surely will, and soon.

“There’s a lot of ebullience and a broad, at the moment, participation of retail investors [in the markets] in a very speculative way,” one senior Wall Street executive told me the other day. He was scratching his head about how there could be a low trading-volume day for big technology stocks but a “massively” high-volume day in the trading of tech stock options. What did that signal, I wondered? “It tells me retail investors are implying volatility and they really shouldn’t,” he continued. “I don’t think it’s different this time. The air will come out and it will force a lot of retail players that have been participating [to rethink].”