Steve Denning, tearing apart Porter’s canonical MBA theory of Five Forces:

How did all this happen? Porter began his publishing career in his March-April 1979 Harvard Business Review article, “How Competitive Forces Shape Strategy”, with a very strange sentence: “The essence of strategy is coping with competition.” Ignoring Peter Drucker’s foundational insight of 1973 that the only valid purpose of a business is to create a customer, Porter focused strategy on how to protect businesses from other business rivals. The goal of strategy, business and business education was to find a safe haven for businesses from the destructive forces of competition.

Ironically, the firm that Porter founded is in bankruptcy. Denning has an interesting take on why it fails: the five forces focus on competition, not on customers. Porter developed the theory based on data from the 1950s, a time where barriers to entry tended to be high in most industries. The internet clearly changed that.