Eric Sevareid (1912-1992), the author and broadcaster, said he was a pessimist about tomorrow but an optimist about the day after tomorrow. Regarding America’s economy, prudent people should reverse that.

This Wednesday, according to the Financial Times’s Robin Wigglesworth and Nicole Bullock, “the U.S. stock market will officially have enjoyed its longest-ever bull run” — one that rises 20 percent from its low, until it drops 20 percent from its peak. And Sept. 15 will be the 10th anniversary of the collapse of Lehman Brothers, the fourth-largest U.S. investment bank. History’s largest bankruptcy filing presaged the October 2008 evaporation of almost $10 trillion in global market capitalization.

The durable market rise that began March 6, 2009, is as intoxicating as the Lehman anniversary should be sobering: Nothing lasts. Those who see no Lehman-like episode on the horizon did not see the last one.

Economists debate, inconclusively, this question: Do economic expansions die of old age (the current one began in June 2009), or are they slain by big events or bad policies? What is known is that all expansions end. God, a wit has warned, is going to come down and pull civilization over for speeding. When He, or something, decides that today’s expansion, currently in its 111th month (approaching twice the 58-month average length of post-1945 expansions), has gone on long enough, the contraction probably will begin with the annual budget deficit exceeding $1 trillion.