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.

Wall Street closed flat on Friday, hovering near the previous session's record-high close for the Dow and S&P 500, while the dollar firmed as investors digested the Federal Reserve's 50-basis-point cut midweek that started a rate reducing cycle.