Accountability is an important aspect of building and maintaining Trust: It is the way in which we answer for our own actions and decisions, taking responsibility for the outcomes.
Accountability should also be reciprocal: It only works if both parties are willing to account for their responsibilities.
In order for accountability to exist, there needs to be an explicit clarity and agreement on expectations: I can't be accountable for an expectation that hasn't been shared with me, or one I haven't agreed to.