Any discussion of secular stagnation needs to divide the conversation into three parts: long-run growth, the deviation or gap away from the long-run (cyclical), and level changes in growth. Confusion arises when the discussion does not make a distinction between these three. Any discussion of output gaps, inflation, natural rates of interest and unemployment all have to account for economic growth trends, cycles, and levels
On top of this backdrop there is the fact that monetary policy, through excessively low rates, will increase the chance of bubbles which may mask these secular trends. How can you trade stagnation when a bubble is pushing asset prices higher? You have to embrace bubble risk. Clients demand return, so the short-run cannot be forgotten. This is a sobering story, but one that has to be digested.