" Fair is foul, and foul is fair"
In act one scene one the witches say "Fair is foul, and foul is fair." This quote means that whatever is pretty is to turn ugly and whatever is ugly can be pretty. What they do can be the opposite to what appears to us. This also could mean that whatever Macbeth does in his life can become a bad outcome. He will than do that he thinks to be fair or foul disregarding what could be fair to him.