stock
Generally a stock's price reflects the company's future earnings potential. This can be anywhere from a quarter to years down the road. If an investor knows that the company is growing and will continue to grow, the stock is more attractive to them and thus the price of it goes up. This is what happened when apple's shares went up to the $700s a while back as investors predicted that apple would continue to grow at or above the pace it was growing. We know no that apple is facing some pressure by the android OS and recent QE reports show slowed growth. When slowed/no growth occurs, a stock price correction occurs as investors try and flee as they now know the stock is over valued. Investors sell their shares, prices go down. More investors get scared and try and sell and then you end up with apples shares bottoming in the upper $300s last year. Knowing apple is a well managed company by Tim Cook, a smart investor would've bought stock during that panic as apple stock tumbled.