I suspect, that you have taken it into your head, in most cases, that the matter is all, and the manner little or nothing. If you have, undeceive yourself, and be convinced that, in everything, the manner is full as important as the matter. If you speak the sense of an angel, in bad words and with a disagreeable utterance, nobody will hear you twice, who can help it. If you write epistles as well as Cicero, but in a very bad hand, and very ill-spelled, whoever receives will laugh at them; and if you had the figure of Adonis, with an awkward air and motions, it will disgust instead of pleasing. Study manner, therefore, in everything, if you would be anything. My principal inquiries of my friends at Paris, concerning you, will be relative to your manner of doing whatever you do. I shall not inquire whether you understand Demosthenes, Tacitus, or the Jus Publicum Imperii; but I shall inquire, whether your utterance is pleasing, your style not only pure, but elegant, your manners noble and easy, your air and address engaging: in short, whether you are a gentleman, a man of fashion and fit to keep good company, or not; for, till I am satisfied in these particulars, you and I must by no means meet; I could not possibly stand it. It is in your power to become all this at Paris, if you please.
Source: Letters to His Son by the Earl of Chesterfield, p.355-356