Macbeth becomes overconfident after receiving the prophecies from the apparitions conjured by the witches. The first, an armored head, tells him to beware the Thane of Fife, but the next two, a bloody child and a child wearing a crown, tell him that he cannot be killed except by a man "not of woman born," and then only when "Great Birnam Wood to high Dunsinane Hill sahll come against him." He responds confidently:
Rebellion's head, rise never, till the Wood
Of Birnam rise, and our high-placed Macbeth(110)
Shall live the lease of nature, pay his breath
To time and mortal custom.
Despite these assurances, Macbeth still feels it necessary to kill Macduff, (the Thane of Fife) but because he is not at his castle, he survives, but his family does not. It is difficult to say that his overconfidence caused his death, though. Rather his relentless ambition, which drove him to commit one murder after another, seems to be to blame. His overconfidence made him believe that he would be victorious, but given the extent to which he had alienated the important men of Scotland, it is difficult to see what his overconfidence had to do with it.
The witches, Hecate in particular, lure Macbeth into overconfidence with their prophecies, which make it seem impossible for him to lose the battle against the invading army. As Hecate says, it is easy to trick mortals. She tells the witches that they
Shall raise such artificial sprites
As by the strength of their illusion
Shall draw him on to his confusion.
I have almost forgot the taste of fears.