After Duncan, the king of Scotland, names his son Malcolm to be his heir to the throne, Macbeth's disappointment begins to show that he can be dishonest and disloyal. He says,
Stars, hide your fires;
Let not light see my black and deep desires.
The eye wink at the hand, yet let that be
Which the eye fears, when it is done, to see (1.4.57-60)
Macbeth begins to consider what he will have to do to become the king since he isn't going to attain that position in the legal, traditional way. He evidently comes up with some upsetting idea; that he will have to kill the king, his friend and cousin. He asks the stars to go dark so that no one will be able to see the "black and deep" thoughts he is having. He even suggests that he does not want his eyes to see what his hand will do, because it is going to be so terrible. He is obviously contemplating something awful, showing that his ambition may be greater than his integrity and loyalty.
After Macbeth murders Duncan, he turns his sights on his former best friend, Banquo, because the Weird Sisters said that Banquo would father a line of kings and Macbeth doesn't want all of his work to benefit someone else's children. He says,
Our fears in Banquo
Stick deep, and in his royalty of nature
Reigns that which would be feared. (3.1.53-55)
Macbeth becomes disloyal to Banquo and treats him dishonestly when he says that he looks forward to seeing Banquo tonight at his dinner. He orders the murder of Banquo and his son, Fleance, as a result of his disloyalty.