The chart above depicts the overall performance of the S&P 500 against the performance of the three largest companies in the world by capitalization today and at the two major prior price peaks.

The peak in Microsoft shares, at the time the most highly valued company in the world, coincided with the early 2000 peak for the stock market. In 2007, PetroChina played spoiler for stocks. Clearly a similar peak in Apple shares would be a major headwind for stocks today. For that reason alone we should be watching its stock price pretty carefully.

via Abnormal Returns