Needless contradiction - St Francis de Sales

"It was a saying of S. Louis, that one should contradict nobody, unless there was sin or harm in consenting; and that in order to avoid contention and dispute. At any rate, when it is necessary to contradict anybody, or to assert one’s own opinion, it should be done gently and considerately, without irritation or vehemence. Indeed, we gain nothing by sharpness or petulance."