In William Shakespeare's Macbeth, by the time Macbeth writes or talks to Lady Macbeth about the witches' three "predictions," two of them are already true and there is only one left: Macbeth will be king. It is indicative of the couple's greed and ambition that they are not content to let this prediction happen on its own; they insist on helping matters along and they do so immediately.
Their plan--actually it is Lady Macbeth's plan--is to kill the current king, Duncan, while he is a guest in their home. Lady Macbeth will giet the king's guards drunk, Macbeth will kill Duncan, and they will blame the drunken guards for the deed. The plan seems so simple; however, it is not as easy as it sounds to accomplish this murder.
First. Macbeth is not that interested. His wife has to browbeat and insult him into doing the deed.
Macbeth: We will proceed no further in this business....
Lady: Was the hope drunk
Wherein you dress'd yourself? hath it slept since? ...When you durst do it, then you were a man.
He is finally persuaded (bullied) into the plan, but even then, he cannot kill Duncan at first. He experiences a mirage with a bloody knife and feels extreme guilt just at the thought of committing the deed. He is finally forced to kill Duncan himself because Lady Macbeth, ironically, could not do it because Duncan looked too much like her father as he slept. Not only does Macbeth commit Duncan's murder, but he goes a little crazy and kills the two guards, as well.
The suspicions begin almost immediately; however, Macbeth and his wife soon achieve their goal and, on a dark day for Scotland, are crowned as king and queen.