The exception to this rule is social internet companies. Social companies are built in a day and can die in a day - we've seen it happen again and again, and Facebook's scale is no protection.
To beat Verizon, you need a network. To beat Google, you need search technology, data, and great engineers. To beat a car company, you need some factories.
But to beat Zuckerburg, all you need it timing and a good strategy, and equivalent engineers. And in this case, Google seems credible on all fronts.
This is the first serious threat to Facebook's existence.