 While habits may become routines, Dewey argued against the assumption that they were therefore automatic or insulated from conscious intervention. They cannot be automatic, because new situations vary, and the same exact acts never repeat. Thus, unlike machine routines, organic habits remain plastic, changeable. My habitual eating of sweets is subject to contingency (a sharp toothache) and modification (restraint, substitution); frequently, conscious reflection on an existing habit is the first stage of habit revision.