Alan Greenspan's conundrum is back, and central bankers' new-found love of treating markets with kid gloves is playing a large part.
While the U.S. Federal Reserve is expected to raise interest rates for the third time this year, and officials expect another three hikes in 2018, benchmark U.S. bond yields have remained stubbornly low through 2017 and the gap between short and long-term rates has flattened.
At the same time, stocks have continued on an upward ascent, with the S&P 500 hitting record after record and the Dow Jones Industrial Average breaking through 24,000.