The moral burden, if there is one, is typically on promise keeping and being trustworthy, not on either promising or trusting. That is because the immediate, short-run incentives in relationships of promising and trusting are on the side of failing to fulfill the promise or the trust. The potential promise keeper, however, is first the promiser. I make a promise to you, and I am expected to keep it. On standard understandings of obligation, I impose my own obligation on myself when I promise. The trust relationship is very different. The one who faces the burden of trustworthiness is not the one who trusts. I trust you, and you are the one who is expected to fulfill the trust. But I cannot impose an obligation on you to fulfill that trust. Moreover, it would be odd generally to moralize promising, as opposed to promise keeping; similarly, it should be seen as odd generally to moralize trusting, as opposed to trustworthiness.

Russell Hardin, Trust and Trustworthiness, loc. 324