And I am not saying that most people actively manage their 401Ks/IRAs
In short, we have much more ability to make big moves with significant percentages of our investments than any one fund does.
So we have the ability to move the market but dont use it. That I agree. Investors (401k/ira) react to the market, not move it imo. Imo big money still controls the day to day stock prices of individual stocks (and market in general) much much more then "us"