There are myriad reasons why a stock's price falls and it is up to you as a stock investor to determine the cause. By identifying why the price is falling, you are far better equipped to decide if it is time to sell your stock position or if the fall in value presents an opportunity to purchase additional shares of a stock. The key is neither to react every time a stock you own dips, nor to become so emotionally attached to an investment that you stay with it no matter what the news.
As a long-term investor, you should be aware of any cyclical behavior in a stock's industry before you buy the stock, and you should be prepared to hold the stock through the upward as well as the downward portions
Trying to make your own luck by timing the market is unlikely to work, and letting yourself get excessively swayed by the ups and downs of the headlines is certain to fail.
Markets rise and fall, but history has shown that over the long term a well-diversified portfolio of stocks will not only generate a positive return, but also provide the best opportunity for providing a return above the rate of inflation. It is important to keep your investment horizon in mind—long-term investors should not be deterred by short-term declines. In stock investing there are a few universal truths. One of them is that at some point, a stock's price will fall.