Mr. Romney would be a fool to believe a political campaign is the right place to explain the private-equity business. But he has a perfectly defensible story to tell.

First, the money: He expected to be paid well. But nobody—not even those whose billions earned in private equity make Mr. Romney’s millions look paltry—envisioned the astounding rise in business values in the gilded ’80s and ’90s. When Mr. Romney was asked by his boss to start Bain Capital in 1983, the Dow was at 1086.50. When he left on Feb. 11, 1999 to run the Olympics, it was 9363.46. His is not the only recent fortune owed partly to this accident of timing (Warren Buffett’s and many others come to mind). Indeed, if we’re being honest, Mitt here is representative of a generation of professionals whose serendipity it was to have spent the 1970s on our education and then to be spit into the job market just as one of history’s great economic liftoffs was taking place.

Second, the work: He put his talent for calm, careful analysis to work helping American businesses adapt to the onrushing challenges of globalization and technological change. Looking back, it may even be true that his ratio of jobs created to jobs destroyed was better than the economy’s as a whole.

What does this have to do with the presidency? Perhaps not much, but one thing he didn’t learn at Bain Capital was to twiddle his thumbs because taking action might make somebody mad at him. That’s not the worst qualification to bring to the Oval Office right now.