The phrase "Fair is foul, and fouls is fair" is spoken by the three witches present in the play written by Shakespeare, Macbeth. This sentence is part of the prophecy that the witches give to Macbeth and means that winning and losing depends on the perspective of MAcbeth, he can achieve victory in a fair way, but in a failed way, which makes the victory unpleasant and unfair.
As we know Macbeth manages to take the throne, which was a great desire of his heart, for him it seemed that the crown was just, but in his heart, he knew that his victory was granted by flawed, murderous and terrible methods, which haunted for a long time. However, if he had continued with his normal course, without killing the king and usurping his throne, he would have a life that would seem flawed, but it would be fair.