No one rings a bell at the top of the market and declares that it’s been a nice run, so it’s time to get out. But there’s no denying that the stock market is very frothy these days. (As usual, this is not investment advice.) Both the narrow equity market index (the Dow Jones Industrial Average) and the broader indices (the Nasdaq and the S&P 500) are at, or near, their all-time highs, and have been steadily climbing week after week, month after month, despite the slight pullback this week. And this is not just a Trump II phenomenon, as the president likes to claim. This era of irrational exuberance began at least five years ago, when the Federal Reserve stepped into the Covid fray and resumed its policies of quantitative easing, which boosted the bond market and restored confidence in the stock market. (And if you take a longer view, it’s been going on since the aftermath of the 2008 financial crisis, and maybe even as far back as 1982, when the equity markets really took off after decades of stagnation.) Since March 2020—when Tom Hanks got Covid while filming in Australia and the world shut down—the D.J.I.A. is up 63 percent. During the same period, the Nasdaq is up 165 percent. The S&P 500 is up 126 percent.