The document discusses common mistakes in competitive strategy and obstacles to developing an effective strategy. The biggest mistake is not having a strategy at all. Other mistakes include competing by doing what competitors do instead of finding a unique approach, and overestimating strengths while underestimating weaknesses. Major obstacles to strategy include biases in decision-making, incentives that reward the wrong behaviors, human resistance to change, and external pressures. Effective strategy requires understanding competition, making tradeoffs, and sticking to the strategy despite challenges.