Потому, что по статистике 80-90% водителей считают, что они водят автомобиль лучше среднего.
Цитата:
Illusory superiority is a cognitive bias that causes people to overestimate their positive qualities and abilities and to underestimate their negative qualities, relative to others. This is evident in a variety of areas including intelligence, performance on tasks or tests and the possession of desirable characteristics or personality traits. It is one of many positive illusions relating to the self, and is a phenomenon studied in social psychology.
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Svenson (1981) surveyed 161 students in Sweden and the United States, asking them to compare their driving safety and skill to the other people in the experiment. For driving skill, 93% of the US sample and 69% of the Swedish sample put themselves in the top 50% (above the median). For safety, 88% of the US group and 77% of the Swedish sample put themselves in the top 50%.
http://en.wikipedia.org/wiki/Illusor...riving_ability