Following the market is bad for your (returns)
Scott does a great job here summing up why individual investors are much better served going on "auto-pilot" than they are taking an active role in their investments. Logging in every day, getting emotionally involved with the fluctuations, turning on CNBC, etc - these all lead an investor down a path of worry & fear.
I think Yoda put it best: “Fear is the path to the dark side. Fear leads to anger. Anger leads to hate. Hate leads to suffering.”