Everyone knows that you aren’t supposed to buy high and sell low, but many do it anyway.
The following chart is taken from The Fundamental Index by Robert Arnott, Jason C. Hsu, & John M. West. The chart shows the magnitude of underperformance for the average mutual fund investor.
Successfully investing has more to do with controlling emotions (which generally lead you do do the wrong thing at the wrong time) than anything else.
For that matter, maybe it went up a little too much in price, and now investors are coming to their senses. Fund Investing