There is no such thing as a good influence. Because to influence a person is to give him one's own soul. He does not think his natural thoughts, or burn with his natural passions. His virtures are not real to him. His sins, if there are such thing as sins, are borrowed. He becomes an echo of someone else's music, an actor of a part that has not been written for him.
As one knows the poet by his fine music, so one can recognize the liar by his rich rhythmic utterance, and in neither case will the casual inspiration of the moment suffice. Here, as elsewhere, practice must precede perfection.