I've thought a lot about it too. Investing in "extremistan" - the stock-ticker price of a stock is dangerous. If you are a buyer and seller of stocks, then a 90% drop in the market is a disaster.

But if you are a buy-and-holder (i.e. a buyer of future cash flows), then a 90% drop in the market is a great thing - you can buy a lot more company that before. Regardless of how the market moves, you will still be acquiring an ever-growing % of whatever company you are looking at.

And you have dollar cost averaging working in your favor as well, so you are guaranteed to do at least a little better than average.