Who then shall blame
His pester’d senses to recoil and start,
When all that is within him does condemn
Itself for being there?

– William Shakespeare

Macbeth, Act 5, Scene 2. Menteith believes that Macbeth’s inner turmoil is what is making him act crazy. He paints an image of a troubled Macbeth who is essentially at war with himself because of the unnatural crimes and sins he has committed, including murdering King Duncan. If Macbeth has gone mad, then Menteith says that he has only himself to blame and has brought it upon himself.