Macbeth is about a good man who doesn't know when he is well-off. This is a common state for human beings. We believe we MUST have more, and yet life would be so much simpler if we could just learn to be satisfied with what we have. Sometimes to get what we want, we push others because we believe they can help us in some way, and we don't have to "get our hands dirty." It is not impossible to see one friend trying to get another friend involved in a scheme that may not be the best for the other person (as Macbeth tries with Banquo). Sometimes we want something and will do almost anything to get it, only to find that we really aren't happy with it as we thought we might be, and may have lost friends along the way. Macbeth is a play with characters that reflect our own difficulties, and this is one reason why Shakespeare's plays—and characters—are so timeless.
Macbeth also demonstrates the demand for immediate gratification with which many people in today's society struggle. Macbeth was told he would become King. If one can assume the prediction would come true, then Macbeth and Lady Macbeth should have waited for the natural course of events to occur. They chose a more immediate and less moral path.
Macbeth's weakness, as well as his 'vaulting ambition' is choosing not to see that he cannot change the way things are meant to be, and that there are powers and systems at work which are greater than himself. As humans we may believe that we can change the natural order of things and resolve to fight systems and higher judgements that can thwart us. However, there are natural codes, and possibly those defined by higher forces, which are stronger than ourselves. Like Canute, we cannot make the waves to go back. There are several figureheads in US history (post #1 puts the best example most eloquently) that have believed they are 'above' or 'outside' the law.
Macbeth is content with what he has until something more is offered him. He is swayed by others (his wife) to do what he knows should not be done. He keeps on a path of destruction in his attempts to assuage his paranoia and guilt.
Macduff loves his family but hates what is happening to his country even more. He is willing to make the personal sacrifices he can to ensure the health of the state and the greater goodd of its citizens. His is a righteous indignation and he acts on it.
The characters in Macbeth are representative of our own struggles in a plethora of variant ways. Corruption is an element of the play that runs through nearly every fiber of certain characters from the moment the corruption happens, typically to their demise. Ironically, Macbeth is the primary victim of corruption in the play, and it seems fitting to say that his initial corruption is the springboard for the rest of the events that follow. The corruption comes from the initial desire in conjunction with someone encouraging gaining that desire through corrupt measures, such as cheating on a quiz at school or lying to a friend to get them to agree with you in an argument. Macbeth was corrupted through his wife’s suggestion that he gain the throne by killing Duncan. We, humans, are corrupted through peer pressure, popular culture media, and so many other things- particularly those close to us, hence, Macbeth’s dilemma represented quite accurately in our own lives. There are, of course, many other ways the characters could be representative of the struggles of humanity. Lady Macbeth is a prime example of that on the issue of dealing with guilt. Also worthy to be mentioned is betrayal, which is another recurrent struggle in the play as well as in real-life.