i sell PUT options in the VIX so i follow this closely. This is the volatility index for the S&P index. In simple terms the VIX measures fear in the market. The amount of PUT options traders are buying to hedge themselves against a fall in stock prices. The VIX has been very low for a long time now. There is absolute complacency in the market.
The VIX will always revert to the mean. We saw this level of complacency in 2007 prior to the 2008 crash. The Fed may well raise rates next month, there is the Dutch and French elections, either of which could break the EU. North Korea is launching missiles. There is constant conflict in the Middle East. The stock market is at all time highs without earnings to support these nosebleed heights.
It is speculated that the market is being pushed high so the insiders can get out at maximum profit.
Every parabolic move ends in a similar move down.