If you have doubts about where the market is heading and no fundamental view about direction, one place to search for one is in historical parallels. Sometimes looking at history prompts bullishness, but in this case, looking for past market parallels is terrifying. At the moment, the chart making the rounds is one comparing the current S&P 500 to 1937. Doing so makes it look as though the market is going to revert back into a bearish grip at any moment. But guess what, the same chart floated around in 2010, 2013, and 2015, and the big fall never happened.
FINSUM: This bull run has defied gravity many times, and it is hard to see why his time would be different. That said, all good things must come to an end at some point.