As one of the most famous soliloquies in Macbeth, the dagger scene (Act I scene 7) best show the inner conflict (that voice inside your head that causes you to question your own actions and decisions). In this soliloquy Macbeth stands along on the stage contemplating his task at hand.
If this deed were done when it is done, then it would better
If it were done quickly. If the assassination of the King
Could be entangled with the consequences, then I could,
With his murder, be a success. If only this blow
Could be the be-all and the end-all right here,
Only here, upon this bank and shallows of time,
We’d risk it for the life to come.
Macbeth wants to be king. He wants the titles and power predicted for him by the witches, but as he stands just outside of his soverign's room, he wonders if he is strong enough to commit the deed.
Duncan is here in double trust. First, he is here because I am his relative and his subject, Both Strong reasons against the deed. Secondly, as his host, I should shut the door against his murderer, Not carry the knife myself.
Macbeth realizes the importance of his position. The king trusts him. As his guest, Macbeth should be protecting him- not planning his murder. As his subject, he should be loyal to him- not planning to take his crown.
While he ultimately does kill Duncan, it is only after several moments of self reflection and personal pep talk to persuade himself to follow the dagger (a sign in his mind) ushering him towards the kings room and to his future.