In “Leave It To Jeeves”, Jeeves hatches a plan whereby Corky’s
benefactor uncle (Alexander Worple) can meet Corky’s fiancee, Muriel
Singer, before knowing than Muriel and Corky are engaged, so that
Corky can marry Muriel without his benefactor’s disapproval (and
subsequent loss of allowance).
Jeeves even states his scheme “cannot fail of success”.
Since Muriel ends up marrying Corky’s uncle, it would seem that the
scheme did, indeed, “fail of success”.
However, a closer reading shows that Wooster’s actual request was: “We
want you to suggest some way by which Mr. Worple can make Miss
Singer’s acquaintance without getting on to the fact that Mr. Corcoran
already knows her,” which is exactly what Jeeves does. Wooster does
not specify that the plan must not allow Muriel to marry Worple.
In fact, Jeeves was aware of the possibility of Muriel’s affection
swing, as he notes later “That was always a development to be feared,
sir,” but he didn’t want to take the liberty of mentioning it to
Wooster and Corky.