Final answer:
Lady Macbeth notes that the mistake Macbeth made in committing the regicide was that he failed to complete the deed as planned.
Step-by-step explanation:
Lady Macbeth notes that the mistake Macbeth made in committing the regicide was that he failed to complete the deed as planned. In Act 2, Scene 2, Lady Macbeth tells Macbeth that the attempt and not the actual act of killing King Duncan has confounded them. She says that the plan was for Macbeth to smear the blood on the sleeping chamberlains and leave the daggers with them, but instead, Macbeth brings the daggers with him and even fails to return them to the scene of the murder. Lady Macbeth criticizes Macbeth for not following through with the plan, which has put them in a risky situation.