Possibly he could have overcome them, seeing their evil. But he does not. He really cannot, as there is another critical player who has such influence over Macbeth, it is impossible for him to fight his thoughts. .
Lady Macbeth plays a crucial role in guiding Macbeth. When Macbeth feels he cannot murder Duncan, Lady Macbeth taunts him; she belittles him. "Wouldst thou have that which thou esteem'st the ornament of life and live a coward in thine own esteem"(1.7.45-46). She uses harsh words and demeaning examples to persuade him; she questions his manhood. Her words set him up to feel many emotions: uncertainty, fear, desire, and greed. He has strong feelings for Lady Macbeth and is easily manipulated by her. Like the Weird Sisters, Lady Macbeth places images inside of Macbeth's head showing him what his life will be like when he is King. Macbeth's personality is further altered because he listens to Lady Macbeth. He has become a weakened individual, very vulnerable to her influences. She gets him to see what she wants him to see, and places her own desires for power into his head. Macbeth begins to like the idea of being powerful and the idea of wearing a crown on his head. Lady Macbeth fuels this ambition. Without her taunting, her humiliating remarks, her power over him, it is doubtful that Macbeth would have murdered Duncan. She makes sure that Macbeth doesn't back down by taking an active role in preparing the murder. Once he has killed Duncan, Macbeth begins to feel much insecurity and cannot trust those around him; he becomes paranoid. .
The witches have further prophesized that Banquo's descendants will inherit the throne. Macbeth cannot stand the thought of this and arranges for Banquo and his son to be murdered. Although there is only success with Banquo's murder, Macbeth is now involved so deeply that there is no turning back. He becomes more and more consumed with hatred, desire, and greed.