Macbeth foreshadows his own downfall in Macbeth when he first appears and claims, "So foul and fair a day I have not seen."(I.iii.38) He and Banquo are exposed to the witches' prophesies and Macbeth, whilst excited knows that "to be King Stands not within the prospect of belief"(73-74). He does, however, press the witches for more information. He is aware that the witches "cannot be ill; cannot be good" (131) but it still gives him "earnest of success."(132)
Lady Macbeth, Macbeth's "partner of greatness" (I.v.10) is equally excited and certainly willing to take things to the next level because she is concerned that Macbeth is "too full o'th'milk of human kindness"(14).
It is a recognition of his own "vaulting ambition" (I.vii.27) as being the only motive for killing Duncan, that causes Macbeth to pause and decide to "proceed no further in this business" (32) until Lady Macbeth suggests that he would "be so much more the man" (51) if he indeed does murder Duncan. Macbeth then seems secure in his intent, as long as he does not get caught and "false face must hide what the false heart doth know."(82)
Macbeth, whilst steeling himself to do "the deed" hallucinates and is confused by the images of the dagger and the witches' prophesies. He hears the bell and , almost as if the bell is the trigger "I go, and it is done; the bell invites me"(II.i.62) and he is prepared to commit Duncan "to heaven or to hell."(64)