Investors are that bad. Even us diligent index investors can be pretty bad. Bogle dislikes ETFs, arguing that the ease of trading (over regular mutual funds) encourages people to self-sabotage by chasing gains, increasing trades, and trying to time markets. He's proven that if we left it well enough alone, the majority of us would be far better off in the long run.
I'm learning to not see my investments as money any more--just a mathematical formula which occasionally gets out of whack. Automatic deposit, deposit, deposit, deposit... Oh, it's January--rebalance! Automatic deposit, deposit, deposit.. Oh it's July already?! Rebalance. [Repeat for the next 9 years.]