Ambition

I think Macbeth wants to be king of Scotland but he didn't have the brass to do it. He needed the mental support from his wife lady Macbeth which she did very well. I think she is the real brains behind the operation but if anything happens shes just the innocent wife. Shes smart and is putting on a good cover in case anything hits the fan. Macbeth's ambition is causing him to kill his king and his friends all to sit atop the throne.