Trust in me, trust in you: A social projection account of the link between personality, cooperativeness, and trustworthiness expectations

• Individual differences in trust are insufficiently understood.
• We propose a social projection mechanism in linking personality to trust.
• Correspondingly, trait Honesty–Humility predicted trustworthiness expectations.
• Cooperativeness (i.e., Dictator Game giving) fully mediated this relation.
• An alternative entitlement-based mechanism is ruled out.

Although trust is a key aspect of social behavior, individual differences in trust are not yet sufficiently understood. Addressing this issue, the present study investigated the link between trait Honesty–Humility, behavioral tendencies in economic games, and trustworthiness expectations. Based on a social projection account, it was hypothesized that individuals base their trustworthiness expectations on their own trustworthiness, i.e., their tendency to cooperate (as opposed to exploiting others). As predicted, Honesty–Humility was positively associated with trustworthiness expectations. In line with the social projection hypothesis, this relation was fully mediated through cooperativeness in the Dictator Game, but not through entitlement in the Ultimatum Game. Cooperativeness (as driven by trait Honesty–Humility) is thus an important determinant of individual differences in trust.