不撞南墙不回头...

You can use it as a full sentence to describe someone. You can also use it as an adjective for a personality type. It usually sounds a bit critical. You are basically saying, "Fine, go ahead and fail since you won't listen." It is perfect for that friend who dates the same toxic person over and over. Or a colleague who insists on a broken strategy.

Use it when someone is being irrationally persistent. It works great in casual venting sessions with friends. Use it when you have given up on trying to help someone. It fits well in family arguments where a parent is frustrated with a child. It even works in business if a project lead is ignoring data. It adds a bit of dramatic flair to your frustration.

Do not use this with your boss unless you want to find a new job. It sounds quite blunt and accusatory. Avoid using it for positive persistence. If someone is working hard for a good dream, this is too negative. It implies the goal is a "wall" (a dead end). Do not use it in very formal ceremonies or speeches.

In ancient China, houses usually faced south to get the best sunlight. A "spirit wall" or 影壁 was often built inside the main gate. If you were a guest and didn't know the layout, you might walk straight into it. Turning back only after hitting that wall became a metaphor for being slow-witted or stubborn. It reflects the Chinese value of listening to elders and collective wisdom.

Sometimes people just say 不到黄河心不死. That means "not giving up until reaching the Yellow River." It is very similar but feels more tragic. You might also hear 死心眼 for a stubborn person. But 不撞南墙不回头 is the most visual. It paints a funny, painful picture of a person's stubbornness.