For the second straight summer, the U.S. recovery hit a wall. Unemployment is on the wrong side of 9 percent. The velocity of job creation is one-third of the pace we need to keep up with our growing population. To understand why, let's start at square one: Where do jobs come from?

That's no childish question, but it deserves a simple answer. A job is born when demand grows faster than productivity, either because consumers buy more of the same stuff or because innovations create new stuff....