Macbeth believes the witches because it is an easy excuse for him to foster his "vaulting ambition." Considering that ambition is Macbeth's tragic flaw, Macbeth was not in a situation to further his position more than he had already done before the play begins. Thane of Glamis is a wonderful title, but not as exciting as that of King. It is important to note, however, that it isn't the witches alone who convince Macbeth. To say so would be neglecting one of English Literature's most infamous villains: Lady Macbeth. Macbeth doubts himself (and doubts himself again) before finally being convinced by Lady Macbeth that the witches prophesy should be taken as truth. Lady Macbeth, then, shares a similar tragic flaw with her husband, . . . in fact, perhaps more so.