St. Veronica of Milan
When St. Veronica became concerned about her lack of education, the Blessed Virgin appeared to her and taught her three lessons: Purity of intention, abhorrence of murmuring or criticism, daily meditation on the Passion. Through practice she learned
these lessons and became a saint.
Who would deny that this is a life which hath come down from heaven, seeing it is a life whereof it is not easy to find an example before God came down to dwell in a body of clay. — Second Nocturn, Sixth Lesson
The Imitation of Christ
I am accustomed to visit My elect in two manners of ways; namely, by trial and by consolation. And I daily read to them two lessons: One to rebuke their vices, and the other to exhort them to the increase of virtue.
You notice that one of the three lessons taught this saint by our Lady herself was abhorrence of criticism.
When you are about to say something unkind of anybody, will you remember that you are on the verge of injuring the reputation of one of our Lord's friends? Besides, to say an unkind thing about another proves you a coward of the deepest dye. You are afraid to say this thing to the person concerned and you are not big enough to control an instrument not three inches long.
With my little bow and arrow, I killed Cock Robin.