Bogle may have said that, but that's in the context of his strategy of rebalancing.  Rebalancing the portfolio on some regular basis (mothly, quarterly, yearly) is what makes his strategy of buy and hold work.  It's really not buy and hold because of the rebalancing.  Every time you rebalance, you're buying low and selling high.  Over the long term, you end up with a pretty good return for essentially no effort, no charting, no trying to pick tops and bottoms.

They claim this strategy is not market timing.  That's true, but the rebalancing gives you the advantage of buying low and selling high, which in a sense is a kind of market timing.

What rebalancing is: You decide what percentage of your assets you want in stock, what percentage in bonds, what percentage in metals or commodities.  Most go with just stocks and bonds.  Say you decide for you age and risk tolerance you'll do 50/50 and you'll rebalance every month.  At the end of each month if stocks have gone up, you sell enough to move into your bond etf so that you're back to 50/50.  So you're selling high (stocks) and buying low (bonds).  if stocks tank one month, then when you rebalance, you sell enough bond etf and buy enough stock etf with the proceeds to get back to 50/50.  So you're buying stocks at a discount that month. It's a brilliant strategy in its simplicity!