A record-setting week for Wall Street is closing on a quieter note Friday, and U.S. stocks are pulling back from their highs hit during a worldwide rally the day before. The S&P 500 was down 0.5% in late trading,

"This would be the third time that stocks entered a cycle where annual returns compound at high teens," Fundstrat's Tom Lee said.

For all the nail-biting about the economy over the past year, investors had it easy: a 5% yield on short-term U.S. debt, one of the safest investments in the world. Now, the times they are a-changin’—again.