The Death Of Inflation
Part of the reason why bond investors are paying astronomical prices (buying bonds with zero to negative return) is the built in assumption inflation will stay low forever. Bonds are pricing in a stagnating economy which will keep inflation low.
In the meantime, global stocks are closing in on all time record highs. Stocks are pricing in a surge in global economic growth.
One of these markets will ultimately be wrong (stocks or bonds). The black swan event no one anticipates is that both markets are wrong and mis-priced. In that world, the one I believe we live in today, cash and safety are king.