沉着冷静

You can use it as an adjective to describe someone's personality. You can also use it as a command to tell someone to chill out. It often follows verbs like 保持 (to maintain). Think of it as a compliment for someone who handles a crisis like a pro.

Use it during a difficult exam. Use it when you accidentally spill coffee on your boss. It is perfect for professional feedback or praising a friend's poise. It works well when describing a hero in a movie. It also fits when you are giving a pep talk before a big presentation.

Don't use it for small, happy things. If you are just relaxed on a beach, use 轻松. If you are being quiet because you are bored, this isn't the phrase. It implies there is a challenge to be faced. Don't use it if you are actually being cold-hearted or mean to someone.

In Chinese culture, emotional restraint is highly valued. Being 'hot-blooded' is fine for youth, but maturity is defined by 沉着. It draws from the idea that deep water (沉) flows slowly and steadily. A leader who lacks this quality is seen as unreliable. It is the hallmark of a 'Junzi' or a person of noble character.

You might hear people just say 冷静点 (Calm down) in casual settings. 沉着 is often used in sports commentary. 淡定 is a more modern, internet-slang version of this feeling. But 沉着冷静 remains the gold standard for formal and written praise. It sounds more sophisticated and grounded than the alternatives.