 Google and Apple are both in the S&P 000. Let's say someone buys an iPhone from Apple. They would be unlikely to buy an Android phone and thus Google's operating system is unused. This is just one example of competition. Many other pairs of competitors exist in the S&P 000. The bottom line is when one company succeeds, their competitor may fail. So the net success of the two companies should remain neutral. The net will not grow 00% a year.  