Neil Irwin is a senior economics correspondent for The New York Times, where he writes for The Upshot, a site for analysis of politics, economics and more. His March 16 article is republished here with permission as part of our licensing program. We welcome your comments below.

The 21st-century economy has been a two-decade series of punches in the gut.

The century began in economic triumphalism in the United States, with a sense that business cycles had been . . .