Macbeth's tragic flaw is that of vaulting ambition. When the play first opens, he is a valiant and loyal soldier for the king. However, during his first encounter with the witches, a seed of greed and ambition is planted. At first Banquo and Macbeth tease one another about how ridiculous the predictions made by the witches were. Banquo also admitted that such an evil source could never be trusted to tell the truth. Nevertheless, this is when Macbeth writes to his wife about his encounter with the witches, and this is where is ambition truly rises. It is also true to say, that without Lady Macbeth, Macbeth probably would have remained a true and noble soldier to the king. But, upon reading her husband's letter, she immediately becomes obsessed with the realization of the prophecies told by the witches. It is this very ambition which causes Macbeth to kill Duncan, to kill Banquo, for Lady Macbeth to have killed herself because of overwhelming grief, and which brings Macbeth to his own untimely death.