Aversion therapy is a form of association that gets the person to negatively associate with the things they want to get rid of, especially a bad habit.
Take for instance a person wants to rid smoking. Aversion therapy can use negative association like “the cigarette has a disgusting smell” or “putting the cigarette in your mouth is like putting _______(the thing that the person dislikes eating eg. chillie) into your mouth.
The association of negative emotion to the things you want to eliminate creates pain in your brain, which is totally relevant as it makes you want to avoid that thing.