Sun Tzu's Sun Tzu's strategy teaches that groups are stronger than individuals because we can combine our individuals strengths to negate our mutual weaknesses. The stability of a group depends on two factors: 1) a strongly shared mission (goals and values) and 2) a number of strengths in the other four key areas: climate, ground, character, and methods.
This lesson is useful for understand what presidential candidate's choice of vice-president should and should not do. First, the vice-president must strongly share the presidential candidate's core values and vision, beyond that Obama can strengthen his position by picking someone that supports his weak points in ground (from the south or west) and character (more blue-collar). This makes someone like Webb a good choice. Similarly, McCain, whose weaknesses are climate, and methods, can improve his climate disadvantage, say by picking someone younger, and methods, for example, a better organizer and fund-raiser. This makes someone like Mitt Romney a good choice.