The fast-function part of our brain, that which Daniel Kahneman refers to as System 1, operates mostly in three parts of our brain. Strategy + bus., Spring 2011 at 47, describes each of them briefly. These emanate from deep, primal parts of the brain that evolved relatively early.
One is the basal ganglia, which normally manages such semi-autonomic activities as driving and walking (See my post of May 30, 2006: habits, and the challenge of change, due to basal ganglia.).
The second is the amygdale, a source of emotions and fear and anger (See my post of Feb. 12, 2006: the amygdala hijack.).
The third musketeer is the hypothalamus, which manages instinctive drives such as hunger, thirst, and sex (See my post of Nov. 29, 2011: willpower, glucose and the hypothalamus.).
In-house counsel pride themselves on objective analysis and reasoned decisions. Deep within their brains, three old-world clumps of neurons often make a mockery of that hubris.