The answer is: appearance vs. reality.
In Act 1, Scene 6 from Shakespeare's "Macbeth," Lady Macbeth tells her husband to pretend Duncan is welcome and to look harmless in front of him, although he intends to murder him and take the throne away from him that very same night. In that respect, she does not want Macbeth to look worried or thoughtful when he is around other people; otherwise, it will raise suspicion.