Lack of ability, le-gai qualification, or fitness to discharge the required duty. In re Leonard’s Estate, 95 Mich. 295, 54 N. W. 1082; In re Cohn, 78 N. Y. 252; Stephenson v. Stephenson, 49 N. C. 473; Nehrling v. State, 112 wis. 637, 88 N. W. 610