If you ask a racehorse owner how much he expects to earn on his investment in a year, he will tell you that he does know. The value of his horse is determined by its performance on the turf. The better the horse runs, the more money the owner makes. With stocks and bonds the same principle applies. The value of a stock or bond depends on the performance of the company. If the company makes more money than most people expect, the stock will rise in price. If a company has financial problems, the stock will fall in price. The profit you make on a company investment depends on how the company does. A stock is a little different than a bond. A bond is a loan, with a set interest rate. A stock is a stake in Apple's ownership. If the price goes up, you make more money.