For every buyer, there is a seller. Money can't 'flow' in and out of a stock, only the price changes. Is this applicable in the context of asset classes, for example, money market funds versus stocks? If a portfolio manager sells stocks and buys a money market fund, then wouldn't it mean that money 'flows out of stocks'? Or does the same logic apply, that is, since someone bought the stocks from the portfolio manager, there is technically the same amount of money in the stocks?
If this is true and money flow is impossible unless it is an IPO, then why is money flow cited and considered relevant, everywhere?