泼冷水 (pō lěng shuǐ)

"泼冷水 (Pō lěng shuǐ)" literally means "to throw cold water." This idiom comes from the idea that cold water douses enthusiasm or energy. It's used to describe actions or words that dampen someone's spirits or excitement, much like how cold water would extinguish a fire.

For example:

Nǐ bù yào zǒng shì pō lěng shuǐ, yīng gāi gǔ lì bié rén.
你不要总是泼冷水，应该鼓励别人。
Don't always throw cold water; you should encourage others.

Source:eChineseLearning