Well, the good old dictionary states that while madness is "quality or condition of being insane", insanity is "relatively permanent disorder of the mind", both might seem the same, but it isn't! It is like the difference between anxiety and angst. So then why do we say that we are 'madly in love'?... is love a disorder/ a negative or a temporary emotion? How do you differentiate between a mad man and an insane person? If madness is sudden then how come there is a 'method' to it? Doesn't it unknowingly become a part of us, dying to lash out when it smells the slightest tinge of desperation, anger or sadness that struggles to survive within us?
Is obsession not a shade of insanity? Aren't extreme emotions a part of madness-- sporadic but intense? While watching the movie-- Shutter Island, I was numb. May be that was the Director's intent, to confuse you about how to feel about the film-- thriller, mystery, dark or plain philosophical. Initially, some of the scenes were so metaphorical that it was difficult to correlate them with the normal flow of the film. Towards the end as the plot starts to clears the confusion, the Director decides to leave it to his audience to interpret the whole narration. it left me a bit desperate, I wanted to know the truth from him. What especially left me wondering was the last dialogue of Di Caprio before being lobotomised, "Which do you think would be worse, to live as a monster or to die as a good man?"
Coming back to the subject, is madness or insanity bad, unnatural and out-of-ordinary? I feel its a part of you and your existence. The only difference is that while some acknowledge its presence, others simply deny or ignore their presence in the hope that it would die, not realising that a slightest uncontrolled moment can unleash these instincts and change your life forever.
Our mind so complex, unpredictable, sly and mysterious that if left alone, it can play the dirtiest of tricks on us and that's why you need to listen to your heart as well. Even Severus Snape told Harry Potter that it is easy for others to read your mind and affect you if you do not know how to control it and where to restrict it.
For me insanity arises out of lack of listening to your heart and the inability to master your mind, thus it is not negative. It is a source to remain sane by accepting its elements within you and to remain hopelessly optimistic or practically realistic.
