我难过。

You can use this phrase on its own or add adverbs for intensity. Want to say you are very sad? Use 我很难过 (wǒ hěn nán guò). It functions just like an adjective in English. You do not need the word 'am' (shì) here. Just subject + adverb + 难过.

Use it when you lose something important or fail a test. It is perfect for telling a partner you are hurt by something they said. You can use it in texts when you need a shoulder to cry on. It is also common in Mandopop songs when the singer is heartbroken. If your favorite character in a show dies, this is your go-to phrase.

Do not use this for physical pain like a stubbed toe. For that, use 疼 (téng). Avoid using it in high-level business negotiations unless you have a very close relationship. It is an emotional word, not a professional status report. Also, do not use it if you are just bored. It implies a deeper level of genuine upset.

In Chinese culture, the word 难过 (nán guò) suggests that time is moving slowly because of your pain. The characters 难 (hard) and 过 (to pass) imply that life is a river you are struggling to cross. It reflects a traditional view of emotions as obstacles to be weathered. It is less dramatic than 'depressed' but more serious than 'unhappy.'

You will often hear 心里难过 (xīnlǐ nán guò), which means 'sad in my heart.' Another common one is 别难过 (bié nán guò), which means 'don't be sad.' If you want to sound a bit more modern or dramatic, you might hear younger people say they are 'heart-broken' or 伤心 (shāngxīn). But 难过 remains the most versatile choice for any sad occasion.