a cool head 冷静的头脑（the ability to stay calm and think clearly in a difficult situation）

例句：
These are high pressure situations and you have to keep a cool head.
在高压力的情况下你必须保持冷静的头脑。

Professional trustees are trained to handle hostility and usually manage to keep a cool head.
专业的受托人受过训练来处理敌意，他们通常都能保持冷静的头脑。