We show appreciation because we want another person to know how much we value what they have done. True appreciation is not fake and manipulative; it is freely given without any obligation on either the person doing it or hearing it. True appreciation is an invitation, not an expectation. Showing appreciation invites the other to do likewise sometime in the future. We do not expect the other person to do so. Our appreciation shows we care about the other person and are not doing it for self-serving reasons.