Altria and Target both pay high dividends, but one company's business struggles are far more concerning.Dividend yield is an interesting metric. The math is very simple, but what you can learn from yields is often material. One lesson that long-term dividend investors will quickly learn is that the stock with the highest yield isn't always the best investment opportunity.If you are looking at Altria (MO 0.19%) and its 7.3% yield, you might be better off buying Target (TGT +0.33%) and its 4.5% yield. Here's ...