The history of leading stock market indicators, like the Standard & Poor's 500 (S&P 500), is littered with stories about prices shattering new records as well as precipitous plunges in value. For example, soon after a new high is reached, a major correction could occur, reflecting the inherent volatility and uncertainty of the market.

This can end up being both good news and bad news for market timers.

Market timing is the practice of selling stocks and mutual fund shares ahead of projected declines and buying back those investments when the investor expects the stock market to climb. It's a tempting proposition, and when it works, it can reduce losses and position a portfolio for future gains. However, it usually doesn't work, and getting the timing wrong can result in big losses, from selling shares that would have recovered or from being out of the market when prices rebound.

Market timing appeals to investors who think it can bring them the best of all possible worlds—letting them buy low and sell high. But it's not for inexperienced investors, and even those who know what they're doing and who have all of the resources to help them make intelligent, well-informed decisions are just as likely to fail as they are to succeed.

Not only is the stock market volatile, it is unpredictable. Events like Brexit can have an impact, either positive or negative, on a company, industry, or sector. Market timers think they know better than others what's coming next. Although they may guess right sometimes, they're bound to be wrong, too. To compound the problem, those who are successful once may start to think they are invincible. Of course, they're not.

But just because market timing is generally a loser's game doesn't mean you always have to sit idly by while markets fluctuate. Tactical adjustments may be in order depending on what's in your portfolio, what your goals are, and your investing timetable. However, by investing for the long term and periodically rebalancing your portfolio, you can focus on specific objectives in a consistent manner. This could be especially important following a period of extreme volatility such as the ones the markets experienced earlier this year. Working toward your long-term goals also takes emotions out of the investing equation.

When you engage in market timing, you effectively have to be right twice—getting out of the market at the right time, before a downturn, and then getting back in before the market rallies. That's much less likely to pay off than staying in the market over the long haul—which also happens to be a lot easier on the nerves.