How biases come about in your brain.

if you have a 'bad' experience, there is a leveraging up of the heart rate, contraction of  the gut, and weakness is induced in the muscles etc to register that feeing and the feeling becomes embedded or associated with the event. If that event  is subsequently thought about or pondered, the brain will run a simulation reliving the feeling of the event.

Those feelings then serve to direct  subsequent decision making towards a bias.

If your experience in your past has been  'good', naturally, the opposite physiology occurs.