From Rudyard Kipling’s An Interview With Mark Twain:

… This naturally led to a discussion on conscience. Then said Mark Twain, and his words are mighty and to be remembered:

“Your conscience is a nuisance. A conscience is like a child. If you pet it and play with it and let it have everything that it wants, it becomes spoiled and intrudes on all your amusements and most of your griefs. Treat your conscience as you would anything else. When it is rebellious, spank it — be severe with it, argue with it, prevent it from coming to play with you at all hours, and you will secure a good conscience; that is to say, a properly trained one. A spoiled one simply destroys all the pleasure in life. I think I have reduced mine to order. At least, I haven’t heard from it for some time. Perhaps I have killed it from over-severity. It’s wrong to kill a child, but, in spite of all I have said, a conscience differs from a child in many ways. Perhaps it’s best when it’s dead.”