he's not medically proven, he felt guilt the beating and his head was not real, so killing a man because he was annoying you in a sense is still not a valid excuse but he did have a reason
In Shakespeare's Macbeth, Act 4, scene 1, lines 97-105, Macbeth receives three apparitions which provide him with three pieces of a prophecy (1- Beware of Macduff, 2- Macbeth cannot be harmed by someone born form a woman, 3- Macbeth will not be defeated until the Birnam Wood walks to Dusinane Hill). After hearing this prophecy, he feels pleased and safe to know that he will be king until the day he dies (lines 103-105: <em>"... Macbeth</em><em>Shall live the lease of nature, pay his breath To time and mortal custom."</em>). However, he is still eager to know if Banquo and his offspring will reign eventually (lines 105-108: <em>Yet my heart Throbs to know one thing. Tell me, if your art can tell so much: shall Banquo’s issue ever Reign in this kingdom?</em>). This goes to show that he didn't feel like he had enough with knowing he would be king for his entire life, he also had to know that Banquo would not reign. This shows how irrationally ambitious and egotistical he had become.
It can emphasize setting, highlight a character trait, and draw attention to a seemingly minor detail
