In market legend traders take naked directional positions and make their fortunes by predicting the future. According to theory, this is an impossible task.
The trading industry won’t have you believe this because their pay checks often depend on the imaginary gift of calling market direction. The history of Wall Street is strewn with amazing traders that were genius and massively profitable when the trend was with them but crashed and burned when the trend got to a bend in the end.
So what do you do when you are a financial institution that the Federal Reserve offers infinite money to for almost free? You’d better find yourself a way of trading with that money that isn’t going to blow up, that you can get quickly back, and that pays a fat coupon beyond what the Fed is going to charge you.
You need a "carry trade" (borrowing at a low interest rate and investing in an asset that provides a higher rate of return). You need lots of "carry trades." With trillions on offer almost any trade will do.