In Act 3, Scene 4, Macbeth and Lady Macbeth have a feast with company. Macbeth ruins the party when he sees and speaks openly to Banquo's ghost. It is open to interpretation whether Banquo's ghost is real or Macbeth's hallucination. In either case, Macbeth is the only one who can see the ghost. Knowing that Fleance has escaped, Macbeth is affected with guilt and fear. If the ghost is a hallucination, Macbeth is subconsciously deluding his senses; his guilt and anxiety manifest in this hallucination.
Lady Macbeth excuses her husband, telling the guests that this is simply a common spell that Macbeth has from time to time. When she reprimands Macbeth for spoiling the party and allowing his anxiety to get the better of him, Macbeth concludes that he acts this way because he just hasn't had enough life experiences being a deceitful murderer. Here again, Macbeth is deluding himself, but more consciously this time. He determines that it is not guilt and fear that are making him anxious; he thinks he is anxious because he just hasn't gotten used to being a murderous tyrant of a king:
Come, we'll to sleep. My strange and self-abuse
Is the initiate fear that wants hard use.
We are yet but young in deed. (III.iv.171-73)