This is going to be an over-simplified explanation of how we've got to this point. Some factors I'm going to ignore or dismiss because I believe they are minor factors. You are free to disagree.

Eight years ago the central banks of the world embarked on a bold experiment. They approached the economic crisis with the assumption that it could be fixed with monetary policy alone. Their primary weapon was quantitative easing (QE).
Now, in 2016, experimental monetary policy has run up against reality. The reason is something simple to understand, and yet hard to believe:

central banks are running out of things to buy.

Chairman Lord Jacob Rothschild of Rothschild Investment Trust recently made an interesting announcement.