I have a fairy by my side Which says I must not sleep, When once in pain I loudly cried It said "You must not weep" If, full of mirth, I smile and grin, It says "You must not laugh" When once I wished to drink some gin It said "You must not quaff". When once a meal I wished to taste It said "You must not bite" When to the wars I went in haste It said "You must not fight". "What may I do?" at length I cried, Tired of the painful task. The fairy quietly replied, And said "You must not ask". Moral: "You mustn't.
Lewis Carroll
poem