I can only tell you what I learned from it personally. "Act rationally and carefully, so you won't suffer the consequences". Macbeth's own ambition and pressure from the 3 witches and his wife led to his downfall. If he acted rationally and didn't let the pressure get to him, he wouldn't have been consumed by all that greed and killed all these people for his own benefit, only to be killed by Macduff at the end