But imagine you are a rational individual and you look at an US centric index that tracks the total market and see that you have been in a 11 year bull market where it rose 300%.
Now you look at the ratio between the total market cap and the GDP (also know as the buffet indicator) and see that it's at historical highs and last time it was at this value was just before the last recession.
Sure... the craziness could go on fuelled by irrational optimism, negative interest rates and the feds printing money like crazy. It could and probably will for a while but is it irrational to be prepared for the potential crash?