What ails Neddy Merrill? Alzheimer, Dementia, Amnesia or is it simple and plain Obduracy! The story is intriguing as we are left clueless till almost the middle. There is of course an authorial comment on human obduracy ( which is generally)susceptible to common sense preceding an actual hint from Mrs. Halloran when she commiserates on his misfortune of having had to sell his house. He denies it and in fact her sympathy sounds preposterous because he says his daughters are staying at home. The suspense is sustained very carefully till the end. Neddy completes his pledge by finishing the cross country swim and an exhausted Neddy reaches and finds it empty, dark and locked.
The story is sad and evokes sympathy for Neddy. Whatever the problem Neddy suffered from, it was definitely not obduracy. As for as the other possibilities are concerned, his misfortune could have caused it and left his mind unhinged.