Appearance and reality

The theme appearance versus reality is a general theme in Macbeth. Throughout the whole story it’s very difficult to tell whether a person has good or bad intentions; whether he or she is real or has a false appearance. And it's not only persons who can have a false front. It can also be predictions or psyche playing tricks on you.
"Fair is foul, and foul is fair"
The theme is already being introduced in the 1st scene (the prologue) when the three witches talk about fair versus foul in the line “Fair is foul, and foul is fair.” From this quote one can conclude that it’s very difficult to figure out if something is really fair or foul; they are mixed up. Nothing is what it seems.
Characters' false appearance: Macbeth and Lady Macbeth
Two great examples of characters with a false appearance are Macbeth and Lady Macbeth. They seem innocent and completely loyal to the king, Duncan, during his visit, but really they are carrying murderous thoughts. Actually, Lady Macbeth is telling the audience this by saying to Macbeth: “Look like the innocent flower, but be the serpent under it.” That means that the audience is quite aware of their duplicity during the play.
Meanwhile King Duncan isn't, and in the end this naivety causes his death. His first mistake is making Macbeth Thane of Cawdor because of his believe in Macbeth's loyalty. Actually, he has made this mistake before: The former Thane of Cawdor betrayed him. From the following quote you can tell that king Duncan couldn't see pass his false appearance and therefore trusted him fully:
"There's no art, To find the mind's construction in the face:
He was a gentleman on whom I built, An absolute trust." (Act 1, scene 4, page 27)

From this one can conclude that it can be quite difficult to tell the difference between appearance and reality.
Deceptive predictions
As mentioned earlier, not just characters but also predictions can be deceptive.
The three witches' promises "None of woman born shall harm Macbeth" and "Fear not til Birnam Wood come to Dusinane" are great examples of exactly this. From these it seems as if Macbeth never has to fear. But it’s an illusion. They do come true even though it seems impossible. But then again: Nothing is what it seems.
Your own mind can deceive you!
Furthermore also your mind can trick you to believe that something imagined is actually real. For example; when Macbeth sees the dagger before him he really can't tell whether it is real or just his psyche playing tricks on him. Or when Lady Macbeth has got insane a while after their murder on Duncan she tries to wash the imagined blood of her hands. In this case she truly believes that the blood is real.
So remember...
According to this theme Shakespeare's message is that appearances can be deceptive. Therefore remember: You cannot trust everybody. Some may have bad intentions but are hiding them behind a false front. Appearance and reality do not always match (?).