holding stocks as they go down in price does not necessarily matter. It only matters at time of sale. Selling an index (or a particular stock or set of stocks) as they go down only to buy them again later is not the right strategy... you're incurring transaction costs at the very least and the fact that you cannot time the market means you'll probably lose out even further.

Hold the index, unless you need the cash flow or forecast that you need more buffer for flexibility and don't want, in the short term, to be penalized for volatile stock prices (e.g. in case you need to sell to service some cash needs).

And if you have the cash, continue to buy the index on the way down. If your view is that the market, over the long term, is the best generator of wealth, then continuing to buy into it is the more rational strategy.

Inaction is sometimes the best action. There are more ways to be dead than being alive.