Conventional wisdom says trying to time the stock market is a fool’s game. And if you look at market timing very narrowly, defining it as a discipline that nobody really practices, then the conventional wisdom is right.

Critics of timing like to say that if timing took you out of the market during only the very best days or the very best months of some longer period, your performance would suffer enormously. And of course they are right.

This fall, Barrons magazine published a graph showing the hypothetical results of investing in the Standard & Poor's 500 Index in February 1966 through late October 2001. During that period of almost 36 years, an investment of $1,000 in the index would have grown on a buy-and-hold basis to $11,710.

Then, citing a study done by Birinyi Associates, an investment research firm in Connecticut, the article reported that if an investor missed just the five best days every calendar year, that $1,000 investment would have shrunk to $150.

To anybody unfamiliar with timing and not used to thinking carefully, that statement would be convincing evidence that timing is truly a fool’s endeavor. Why would anybody even dream of taking the risk of giving up a gain of $10,710 and replacing it with a loss of $850?

Recognizing the nonsense of tracking an imaginary timing system that kept investors on the sidelines during only the best five days of each year, analyst Laszlo Birinyi Jr. went a step further. Nobody would knowingly devise or follow such a system, which would be extremely counterproductive.

What would happen, Birinyi asked, if a timing system could be invested in all but the very worst days each year? He found that a $1,000 investment in the S&P 500 Index that missed only the five worst days each calendar year would have grown to $987,120.

Nobody, of course, has been able to devise any system that could weed out the very worst days of every calendar year.

But the contrast between all-but-the-best – an investment that falls to $150 – and all-but-the-worst – the same investment rising to $987,120 – is interesting. I think it suggests that the opportunity to miss the worst days is greater than the risk of missing the best days.

And missing the worst days is exactly what market timing strives for. I wish I could tell you we have a timing system that would let investors miss only the worst days of every calendar year. We don’t, and we never will.

But market timing usually gets investors onto the sidelines during more bad days than good days. And by doing so, it inevitably reduces the risk of being in the market. As we saw in the bear market of 2000-2001 and again in late 2007 and throughout 2008, that can be worth a lot.