Final answer:
Lewis's change of attitude towards proofreading is best explained by self-perception theory, as he observes his own behavior and infers a positive attitude towards the task.
Step-by-step explanation:
The change in attitude that Lewis has experienced after deciding that proofreading isn't so bad after all can best be explained using self-perception theory. This psychological theory suggests that people develop their attitudes by observing their own behavior and concluding what attitudes must have caused them. As Lewis does not have a prior strong attitude against proofreading or a reward to justify his engagement in the task, self-perception theory posits that he infers his attitude from his own behavior, which was engaged and meticulous, leading him to revise his earlier dislike for proofreading to a more favorable view.