On an individual level, the most powerful ability is to leverage yourself by getting others to work for you, by whatever means cost you least time and effort (for example, defrauding or deluding them, paying them if you've the means, coercing them if you have a gang or an army). An individual's time and physical abilities are extremely limited, no matter how smart or rational a person is, he can only work so long and can only be in one place at a time. Until intelligent agents come along, using people is the only way to significant power, the more people the better.