Leaders of enduring firms know the external environment of their firms in order to adapt and anticipate its evolution. They analyze the opportunities and threats that arise to better exploit or counterattack them. Six categories of influences shape the environment in which any organization operates: political, economic, socio-cultural, technological, environmental, or ethical. They are not independent but are interconnected to make up a complex environment. Durable companies have all survived countless battles with their direct and indirect competitors. They were able to eliminate their major rivals of any kind. To achieve this dominance, they identify and survey various competitors to assess their capacity to inflict harm. They take account the asymmetry of competition and the Doppler Effect which can impact the perception of the competitive situation. As a consequence they may choose the opponents with whom they want to fight at a given time. Confronted with competition, enduring firms apply the principle of rational audacity, combining boldness and courage with prudence and defense. Their competitive strategy also evolves with time depending on their relative size and influence in the market. When small, they avoid competitors or they apply the principle of concentration. Once they are larger, they exploit weak points of the rivals with flank attack. Next they concentrate their effort to make a decisive assault. Once they have won, they consolidate their dominance by suffocating their smaller contenders while making temporary alliances with larger competitors.