If interest rates are high, stock prices sometimes go down because it is more expensive for companies to borrow money. Another factor is time of year. Many stocks are seasonal, meaning they do well during certain parts of the year, and worse during others. Companies that produce cooling fans should sell a lot of fans during the summer months, possibly causing the stock price to increase. But during the winter, when people are not interested in being cool, the price of the stock could decrease.
Publicity also has an effect on stock prices.
If an article comes out in the newspaper saying that a company has invented a new product that will revolutionize the industry, odds are the value of that stock will increase. If an article comes out saying that a company is in trouble, the value of the stock will probably decrease. The two worst declines in the stock market came in October 1929 and October 1987. The first crash, which began the Great Depression, saw the market decline 12.8 percent. The second crash, which has become known as Black Monday, saw the market decline 22.6 percent.