Keep a cool head

Origin

The concept of 'cool' as serene and collected has deep roots in English. Historically, a 'hot head' was associated with passion, anger, and impulsive behavior, influenced by ancient humoral theories that linked emotions to bodily temperatures. In contrast, a 'cool temperament' signified rationality, calm, and self-control. By the 18th century, the idiom 'keep a cool head' had firmly established itself, vividly evoking the image of someone who could maintain internal stability and prevent their emotions from boiling over. It’s a powerful metaphor, suggesting that a steady mental 'temperature' is crucial for clear thinking and effective action, especially when faced with pressure.