Too Short of a Time Horizonby Jay Yoder
If you are saving for retirement 30 years hence, what the stock market does this year or next shouldn't be the biggest concern. Even if you are just entering retirement at age 70, your life expectancy is likely 15 to 20 years! If you expect to leave some assets to your heirs, then your time horizon is even longer. Of course, if you are saving for your daughter's college education and she's a junior in high school, then your time horizon is appropriately short and your asset allocation should reflect that fact. Most investors are too focused on the short term.
Source: http://www.investopedia.com/articles/stocks/07/mistakes.asp; http://www.tuckerbrook.com/