Consumer debt is not your friend

Here's a simple MBA lesson: borrow money to buy things that go up in value. Borrow money if it improves your productivity and makes you more money. Leverage multiplies the power of your business because with leverage, every dollar you make in profit is multiplied.

That's very different from the consumer version of this lesson: borrow money to buy things that go down in value. This is wrongheaded, short-term and irrational.

A few decades ago, mass marketers had a problem: American consumers had...