His chart here makes it look like what's been going on since 1995 has been part of one relentless long term uptrend, the sanguine implication of which is that we should stop worrying if we are long term investors:
My chart shows that since the beginning of 1995 the trend supercharged into what people call, for lack of a better description, irrational exuberance, so named by Alan Greenspan himself at the end of 1996, whose own Federal Reserve management arguably makes him the very author of it:
You'd entirely miss that from Felix's chart.
There is no reason why stocks should be down today, as Felix says, except that from the long term perspective an S and P 500 index in the vicinity of 800 looks like a more fair valuation than 1200. The market has twice tried to tell us that, in 2002-2003 at the 775 level, and again in 2008-2009 at the 675 level.
It may be getting ready to tell us something similar again.
What say 575?