UnitedHealth Group's recent stock plunge makes it clearer than ever why we should stop paying so much attention to the Dow.

With the Dow Jones Industrial Average (DJINDICES: ^DJI) sitting around 40,000, it may seem like a big stretch to expect it to reach 1 million at any point. But it isn't as far-fetched as it seems.

On Thursday, the Dow Jones Industrial Average became the latest major U.S. equity-market gauge to experience a “death cross.” It was the first time the ominous signal has appeared on the price ...