The main conflict in "The Possibility of Evil" takes place within Miss Strangeworth's psyche. A strong desire to look perfect—to have the perfect house, garden, china, and silver, and to appear a sweet, kind, and caring person—rages within against the feelings of anger, resentment, loneliness, and aggression she has tried to repress and stuff down. She has denied her negative feelings to herself for so long that she is not in touch with them in any healthy way. She has let them fester while believing herself to be good and pure. Because of her long family history in the town and her outward look of perfection, she believes she is morally superior to her neighbors.

Psychological issues that are left buried have a way of resurfacing. In Miss Strangeworth's case, they emerge in the form of the anonymous poison-pen letters she sends to fellow townspeople, expressing her vitriol in hurtful terms. She both disassociates herself from the letters, using a different stationary to write them and leaving them unsigned, and rationalizes them as a necessary evil.

Miss Strangeworth is an angry, negative person filled with seething resentments. The story suggests, though it does not state, that her loneliness, lack of having married or had children, and sexual frustration might drive her resentments: for example, she refers to a neighbor's baby as an "idiot" and accuses people of having affairs. Miss Strangeworth is a person in conflict with herself who turns to destructive behavior because she has never accepted or integrated her own shadow side.