Liz, who is very warm and friendly, is the life of the party. In fact, Liz invites friends over for parties or cookouts every weekend that she is free (i.e., when she’s not involved with a book club, painting class, or yoga retreat). Liz’s husband dreads it when she invites friends over. He is reserved, uncomfortable with people he does not know well, and prefers quiet evenings of reading. The Big Five trait that best describes this aspect of his personality is ____.