"Fair is foul, and foul is fair" is the most famous and perhaps the most significant line in Shakespeare's Macbeth. This is one of the last lines spoken by the three witches in Act I Scene I, when they are foreshadowing the events that will come in the play. This line is a paradox or an idea that contradicts itself and many interpretations were made to explain what it means.
For me, this line pertains to one of the themes of the play which is the difference between appearance and reality. To put it simply, the difference between how something seems and how something really is. It is a major concern that fits well with the medium of the play and it shows that there is no significance of good and bad for their roles can be reversed.
I also had a personal experience related to this line. It happened 3 years ago. I was just a freshman at Cavite National Science High School and I didn't know anybody there except my classmates during elementary. I didn't want to interact with my new classmates because I felt really shy and it seemed like they all know each other. I also had a lot of first impressions. I thought that they were all serious and competitive and I also thought that some of them were unfriendly. But as I spend more time to get to know them, I realized that they are all nice people. They are really funny and friendly and they are the type of people who you can call real friends. Yes they can be serious and competitive sometimes but they are always there to help me whenever I need them. Just like what people say, first impressions aren't always true.
Fair and foul can be different in various perspectives. Like something bad for someone could be something good for the other. A lost for one would give victory to others. "Fair is foul, and foul is fair". It is a world where things aren't what they seem to be. A world where you're never sure which is appearance and which is reality.