Destiny

The Fates are three goddesses in Greek mythology. According to the legends, our lives are predestined and cannot be altered by our efforts. The three weird sisters in Macbeth predicted Macbeth's rise to the throne and the first steps of succession happened immediately without any effort on his part. Do you suppose he would have been king anyway and could have avoided the bloodshed and resulting guilt?

Regardless of the portents of the witches and the influence of an ambitious wife, Macbeth knew he would be primarily responsible for his own downfall:
In Act I, scene vii, he says:

"We still have judgment here, that we but teach
Bloody instructions, which, being taught, return
To plague the inventor.This even-handed justice
Commends the ingredients of our poison'd chalice
To our own lips."