You're right but it doesn't mean that it's not a zero sum game. When you buy a stock you do not assume it has perfect liquidity (if you wanted that you'd inves

You're right but it doesn't mean that it's not a zero sum game. When you buy a stock you do not assume it has perfect liquidity (if you wanted that you'd invest in a more liquid investment). So you trade liquidity for growth. Liquidity correlates strongly with volatility. If (as you approach retirement) you decide to trade growth for liquidity and convert to cash, you may end up penalized if the volatility of the stock reduces your return (if you have to sell in a dip). This is part of the trade off that you entered into and you are not penalized as long as you can afford to wait out whatever volatile price movements make the conversion temporarily disadvantageous. As for your point 2, while this is true for an individual trade it's the sort of thing that averages out over time...