The only thing motivating Macbeth to kill Duncan is his 'vaulting ambition', like a horse jumping over an obstacle (metaphor)

Duncan is too kind and generous making him not a good King as he is weak

Malcolm is powerful but also generous so he combines the good qualities of both Duncan and Macbeth

Macbeth can't accept that Banquo's descendants will become Kings after him so he has Banquo and Fleance murdered

He is also not willing to share some power with his wife as he keeps making secretive decisions and apparently doesn't care when she dies