Final answer:
Predicting changes in stock prices to earn a quick profit by buying low and selling high is false.
Step-by-step explanation:
The idea that stock prices are based on expectations about the future has a powerful implication. If expectations determine stock price, then shifts in expectations will determine shifts in the stock price. It is extremely difficult to predict changes in future expectations and choose stocks that will rise in the future. Therefore, predicting stock prices accurately to earn a quick profit by buying low and selling high is false.