No man born of woman shall kill you, an you can not be defeated until Birnam wood reaches the hill.
Macbeth's gut to do what's right is swayed by the witches prophecy as well as his own ambition.
Macbeth becomes cocky and feels he is invincible after hearing witches tell him no man born of women will kill be able to kill him and that he wouldn't be defeated until Birnam wood reached the top of the hill.
Macbeth's is realizing he's done all the work to become king. Only to have set up the kingdom for Banquo's descendants.
Macbeth's pride makes him refuse to surrender causing the men to kill him.
Macbeth's downfall is his ambition. We feel for Macbeth because we too have had ambition that has caused us problems.