This is an old case of trust law. It is being followed in company law too. This is shown Just because it gives a clear eg of how that fiduciary duty work. And how strict it is. Keech was a child and they inherited the lease on a market. Sandford was keech trustee. They were looking after the niece for the benefit of the child. We dont know the circumstance. It is a reported case as it is short on facts. What we know that the landlord refused to renew the lease to keech the child but was prepared to lease to sandford. So keech couldn't take it up but sandford could. Sandford took up the lease and ran the market for many years. When keech became adult, he sued sandford for all of profit he made in that period. He was successful. Court made statement - trustee is the only person of all mankind who might not have the lease. If ur in the fiduciary capacity and smtg arises bec ur exercising the duties set, u simply cant benefit. And order him to disgorge all profit s(means cough up) to keech. It gives indication how strict the rule is in terms of fiduciary not personally benefiting from their position