Each time the S&P 500 has traded more than 12% above its 200-day moving-average, the following correction has not ended until the average itself was breached by price action. Fundamentally, one can tie 'events' to each of these exuberance spikes - in this case, liquidity-turns-into-a-taper - but sometimes historical prices can be a better guide to the human biases for extrapolating trends and building fragility. Given current levels that would mean a 10% drop from current levels to 1516.
(h/t @RonnieSpence)