The yield on 10-year U.S. Treasuries has hit 3 percent. The end is nigh. When this threshold was crossed Tuesday, the financial world went into paroxysms. Headlines lit up, and the Dow Jones Industrial Average plunged as much as 600 points, before recovering to close down 424 points. "The 3 percent level is a big psychological point for investors and has gained huge focus," the head of equities at London and Capital told CNBC. But if your own reaction was a mixture of "huh?" and "what?" don't worry: You're the reasonable one.