Gordon Smith of and Jordan Lee of Brigham Young University's J. Reuben Clark Law School have published an article on discretion in exercising fiduciary duties.
From the abstract:
Discretion is an important feature of all contractual relationships. In this Article, we rely on incomplete contract theory to motivate our study of discretion, with particular attention to fiduciary relationships. We make two contributions to the substantial literature on fiduciary law. First, we describe the role of fiduciary law as “boundary enforcement,” and we urge courts to honor the appropriate exercise of discretion by fiduciaries, even when the beneficiary or the judge might perceive a preferable action after the fact. Second, we answer the question, how should a court define the boundaries of fiduciary discretion? We observe that courts often define these boundaries by reference to industry customs and social norms. We also defend this as the most sensible and coherent approach to boundary enforcement.
The article, Fiduciary Discretion, 75 Ohio State Law Journal 609 (2014), can be downloaded from SSRN here.