Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

One of the most backward things about the stock market is that investors love to see rising stock prices and hate to see falling ones. With the Dow Jones Industrials (DJINDICES:^DJI) down another 50 points as of 10:45 a.m. EDT, adding to the average's declines during the earlier part of the week, many analysts are calling for a further correction as they see the positive market momentum that carried the S&P 500 (SNPINDEX:^GSPC) above the 1,700 level recently giving way to pessimism and nervousness.

But for many investors, falling levels in the Dow spell opportunity. When you look at the most promising stocks in the Dow, you'll note that many of them have risen to such lofty levels that much of the profit potential in their businesses is already reflected in their price. 3M (NYSE:MMM), for instance, has made great efforts to reawaken its innovation-driven growth engine, and investors have anticipated success by bidding shares upward even though recent earnings growth has been sluggish. At 16 times estimated forward earnings for 2014, though, it's hard for value investors to feel comfortable with the lack of a margin of safety 3M shares provide at current levels if the company fails to deliver on its growth promise. By contrast, a falling stock market could make 3M shares more attractive while still leaving the company with the same favorable business prospects.

Similarly, Boeing (NYSE:BA) is sitting on a massive opportunity in the aerospace industry, as airlines spend billions updating their aircraft fleets to cut fuel costs and increase overall efficiency. Boeing now expects total industry aircraft sales of $4.8 trillion over the next 20 years, and the company should be able to reap its fair share of those sales to drive its own revenue growth sharply higher. Recent troubles with its 787 Dreamliner actually gave long-term investors a couple of excellent opportunities to buy shares cheaply, but with the stock having recovered to hit new all-time highs recently, you now have to pay up to take advantage of the Boeing opportunity.

Buy stocks at bargain prices
Admittedly, some people need stock prices to remain high. If you're retired and are drawing down on your investment portfolio to cover living expenses, then higher prices are essential in helping you maintain your standard of living.

But for the larger group of investors who are still accumulating stocks and have no plans to spend down assets in the near future, cheaper prices let you buy a greater number of shares with your money. As those companies grow and prosper, owning more of their shares will give you a larger stake in their overall success -- and greater financial rewards from your investment.