I am pretty sure you did not need to be a genius to know that the market was well overheated by the end of 1999 and a massive downward correction was coming. It was just a matter of when.
In 2008 I watched the Dow go down 200 points a day many days, only to rally when the Fed said something. This went on for about a month in which time the Dow dropped from over $14k to nearing $12k and it seemed like a good time to get the Hell out. I waited until a small rally in response to a statement by the Fed and then bailed. Turned out it was a damn good or lucky move.
This year we are again at record highs in the market and it has been 4 plus years since the last massive downward correction. Which seem to come every 4-5 years in this "bubble" economy. The powers that be are busy pushing wars with Syria and Iran and the GOPers are shutting down the govt and playing games with the debt ceiling. Massive uncertainty. Seems like a good time to be on the sidelines. So far (out a bit over three months) the slide has not come but I am staying the hell out. I will risk losing a possible 10% to 20% run-up to guard against what I see as a more likely 20% plus fall.
Either way, when I am on the sidelines I know what the value of my liquid assets will be in x months time. When you are in the market, you really don't know what their value will be. Now that's risky