Federal Reserve Chair Janet Yellen says she wants investors to be prepared for the possibility that the Fed will raise interest rates sooner than they currently project. Her words are going unheeded.

Volatility across stocks, bonds, and currencies worldwide is close to record or multi-year lows, even after Yellen cautioned last week that the Fed's commitment to keep interest rates near zero for a "considerable time" could change if U.S. economic performance continues to exceed expectations.

This absence of wide swings in trading values reflects investor complacency about the central bank's intentions—and may be too much of a good thing for its policy makers as they consider retreating from years of low-rate pledges that suppressed borrowing costs and fueled a recovery from the worst recession since the Great Depression.