We can see a clear contrast between selfishness and ambition. You can want yourself to succeed and work for something in a healthy way. When you get to a point where you'd hurt anyone to get to that point you have gotten to the extremities of greed.
We first meet macbeth and he's in battle and he seems ruthless but once out of battle he seems unsure of himself and hesitant even when lady Macbeth goes as far as to challenge his masculinity and call him cowardly.
"Look, how our partners rapt." (1.3) Shakespeare uses Banquo as a way to bring up this idea of how when the witches tell Macbeth he shall be king it is evident he is interested.
The witches tempted Macbeth using the idea of being kind as bait for him to haven he ambition and drive to kill Duncan.
Lady Macbeth also tempted him when she used manipulation as a form of tempting him to want to prove himself worthy, "I dare do all that may become a man; who dares do more is none." (1.7)
We are starting to see him evolve form being hesitant to having a drive strong enough to actually kill Duncan. We see behavior changes usually tend to be constantly progressing gradually or an even trigger a behavior change, and for Macbeth it was both
We watch his character change and after he kills Duncan he seems to have shifted immensely form when it began. He is now being much more impulsive which can be either interpreted to be due to paranoia or just a sort of wanting to be ready and prepared. "False face must hide what false heart don't know" (1.7) at this point Macbeth is putting up an act to prove he is uninvolved in the murder of Duncan, he chooses to lie. And is very quick so speak without thinking through what he is going to say or how it will be interpreted.
If we had to select one other character we thought best bonded with Macbeth we would pick Banquo. So when Macbeth was hesitant to kill Duncan but then has no hesitation or feeling of remorse at the idea of killing Banquo and his son Fleance we can tell something is off.
"Fleance, his son that keeps him company. Whose absence is no less material to me than is his fathers, must embrace the fate Of that dark hour" (3.1)
Macbeth knows that macduff has no sort of loyalties to him and he feels threatened and angry so he sends a group of murderers to kill him and his family. Macbeths paranoia and greed is driving him to his point. By trying to be secure all it is doing is adding more suspicion to him and at this point lady Macbeth does not agree with him and this is a drastic change from before he murdered Duncan.