Comment by H i s o k a on Eternally Regressing Knight - Chapter 19

@H i s o k a I think the reason why he is still sane is because he embraced his situation and used it to his own advantage in reaching his goal. He used it as a means to an end not an obstacle that will destroy him. 

Usually patients with mental illness has a very good prognosis who are fully aware that something is not right with them. 

Unlike those who deny their situation they would go insane because they kept denying their situation.