Macbeth's initial reaction to the witches' prophecies is to show surprise and fear (Act 1, sc. 3, ll. 58-59). This suggests that the thought of becoming king has crossed Macbeth's mind and he fears that these witches have somehow read his thoughts. Later in that scene, ll. 148-150, his reaction to being named Thane of Cawdor shows that he has hopes of becoming king and completely fulfilling the witches' prophecies. Macbeth is ambitious and he lets his ambition rule his better sense. In sc. 7 of Act 1, Macbeth has decided that he will not go through with his wife's plans to kill Duncan so that Macbeth can get the throne and he tells his wife the plan if off. She immediately begins to berate him and essentially tells him that he will no longer be a man in her eyes if he doesn't go through with the plan to kill the king. He gives in to her rather quickly. She is mortal, not supernatural, so he cannot blame the witches for this. He may want to blame supernatural entities for his troubles, but he is the master of his fate, and he realizes this by Act 5. In sc. 5, when he delivers his "Tomorrow and tomorrow..." speech, he knows he's run his life into the ground and that he has no hope of happiness. Even though as late as sc. 8 of that act, he still holds up the witches' apparitions and their prophecies like a shield in front of him, he realizes he's been duped by those witches. It's reasonable to conclude that he also realizes that he had the power to ignore the supernatural beings and create his own fate.