我没听懂。

Simply drop this phrase as soon as you feel lost. You can say it alone or add a polite 不好意思 (bù hǎo yì si) at the start. It functions as a complete sentence. It is like hitting the pause button on a movie. Most people will immediately try to rephrase or speak slower for you. Don't be shy; everyone uses it sometimes.

Use it when a taxi driver gives complex directions. Use it when a waiter explains the daily specials too fast. It is perfect for meetings when a colleague uses heavy jargon. Even native speakers use it when someone has a thick accent. It shows you are paying attention but need a little help. It is much better than nodding and pretending to understand!

Avoid using this if you didn't hear the sound at all. If the room was too loud, use 我没听清 (wǒ méi tīng qīng) instead. That means 'I didn't hear clearly.' Also, don't use it if you understand the words but disagree with the logic. In that case, you might say 'I don't get your point.' Using 我没听懂 implies a language or clarity barrier, not a philosophical disagreement.

In Chinese culture, admitting you don't understand is seen as being 'honest' (诚实). It is often preferred over 'saving face' by pretending to know. However, adding a smile helps keep the atmosphere light. Historically, Chinese has many dialects, so people are used to hearing this phrase. It is a bridge between different ways of speaking. It is a very humble and practical expression.

You can make it softer by adding 对不起 (duì bù qǐ) at the beginning. If you want to be more casual, just say 没听懂. To ask for a repeat, follow it with 请再说一遍 (qǐng zài shuō yī biàn). If you understood a little bit, try 我没太听懂 (wǒ méi tài tīng dǒng). This means 'I didn't quite understand.' It sounds a bit more advanced and nuanced.