Last week, I noted that various forms of the word “unexpected” almost inevitably appeared in news stories about unfavorable economic developments. You can find them again in stories about Friday’s shocking news, that only 54,000 net new jobs were created in the month of May and that unemployment rose to 9.1 percent. But with news that bad, maybe bad economic numbers will no longer be “unexpected.” You can only expect a robust economic recovery for so long before you figure out, as Herbert Hoover eventually did, that it is not around the corner. Exogenous factors explain some part of the...