Jekyll & Hyde is a famous story of polar behaviour, of the notion that ‘every man has two aspects within him – good and evil – which constantly wage war upon him.’ (Wikipedia)
In the tale, Dr Jekyll uses a potion to transform himself in to a monstrous Hyde, who proceeds to commit various hideous acts. Alas, Jekyll cannot control this monster of his own making. Even though the doctor is conscious of the likely consequences of the transformation, the desire to become Hyde grows ever stronger and the point of no return is passed as Hyde consumes Jekyll. The story does not end well.
I think everyone has a Hyde to their Jekyll. In my trading, this dual is essentially between the rational and the viscerally irrational.
Additional relevant quotes:
We are what we repeatedly do – Aristotle
When you act like the barbarian, you become the barbarian – Niles, quoting a young Frasier, in the television series ‘Frasier’.