If you are picking stocks for your own portfolio, then you are competing against all of the smart stock pickers in the world. In fact, when you're buying or selling, there's someone on the other side betting against you.

While it may be fun, this may not be profitable in that you may end up underperforming the stock market as a whole. In fact, there's a greater than 50% chance, you're losing money by picking stocks.

If the number of large capitalization stocks is dropping due to a falling stock market, what can be done? Change the definition of "large cap." That is exactly what S&P is doing.

According to MarketWatch, "For large-cap stocks, reflected by the S&P 500, the value was cut to $3 billion from $4 billion. The S&P set the $4 billion mark on September 25." That makes for two revisions in three months. If the market keeps falling, perhaps that number could drop to $2 billion.

Why move the goal posts? Perhaps because some S&P indexes are based on the definition of large cap. Perhaps it makes people who invest in large cap stocks feel better.

Changing the definition may actually hurt some investors. There are still plenty of companies that have market caps above $4 billion or even $5 billion. There is a sense that the stocks in these firms are "safer" than other equities. A company that has been dragged below the $3 billion threshold may be a company with a stock that has dropped faster than the market in general or it may be a company that has a falling cash balance. A firm with $1 billion of cash on its balance sheet is more likely to have a market cap of over $3 billion than a company that has $200 million. Being a large cap stock actually means something, even if it is only by having balance sheet that is likely to be healthier than many others.

The S&P action will probably confuse some investors in an already confusing market. What is a large cap stock? Whatever S&P says it is.

Douglas A. McIntyre is an editor at 24/7 Wall St.