If I have optimistic expectations I will more readily take risks on the trustworthiness of others, and if others in the context are relatively trustworthy, I will benefit greatly from the cooperation that we can achieve. If, however, others are not trustworthy in the context, I may quickly learn that and will protect myself against betrayal by them. If on the contrary I have pessimistic expectations, I will not readily take risks with others. Hence I may not even gain the experience to revise my expectations when I come into a context in which others would commonly be trustworthy.

Russell Hardin, Trust and Trustworthiness, loc. 614