In a well-known routine from the mid 1970s, the late comedian George Carlin, an astute observer of language, made light of incongruent phrases such as “jumbo shrimp” and “military intelligence.” As a parallel to Carlin's list of words that “don't go together” we might add people in unlikely professions or roles, individuals such as a cautious daredevil, an unreflective philosopher, a disagreeable yes-man, or an introverted motivational speaker. Or, thinking of social and political actors, we might contemplate the rude and uncaring volunteer, the timid lobbyist, or the open-minded ideologue.

These individuals resist imagination because, by their nature, some types of people seem to be poor fits for certain occupations, avocations, and roles. The phrase “by their nature” refers to people's enduring tendencies, or traits. Many students of the psychology of individual differences examine the content and significance of basic traits. In simplest form, such inquiry involves a two-step process: Key differences in traits are identified, followed by exploration of possible relationships between these traits and attitudes and behaviors. Intuition and everyday experience underlie many of the patterns we can envision, in some cases to the point that relationships may seem virtually tautological. For instance, we expect scientists to be systematic, counselors to be sympathetic, and entertainers to be outgoing. But these relationships are not tautological. To the contrary, if we study these possible patterns and the resultant evidence corroborates our expectations, an exercise of this sort would demonstrate that traits matter.