When Vてしまう is used to express that an action is regrettable or undesirable, does it express the opinion of the speaker or the listener? Put another way, when one says Vてしまう, are they expressing that they feel that V undesirable, or that they are under the impression that their listener will find V undesirable?
For example, would it be appropriate for a man to say to his wife (who he knows does not care for her weight at all),「そんなに食べたら、太っちゃうよ！」if he thinks weight is unsightly? He can't be looking out for his wife's feelings, because he knows that she can't care less about getting fat.
On the other hand, would it be appropriate for a man who is wholly accepting to say 「そんなに食べたら、太っちゃうよ！」 to a wife who has once stated a negative opinion regarding gaining weight? In that case, he wouldn't be saying it out of selfish regard, but for hers.