In SC (Chinese wrestling), you can't challenge me if
- you don't have SC jacket on, or
- I don't have SC jacket on.
When we both have SC jackets on (such as in the class environment that both teacher and students all have SC jacket on), if a student challenges his teacher, the teacher cannot refuse. I had 7 of my students challenged me in the past. I was young and I didn't care. Today when I teach a class, I don't put on SC jacket. So, challenge cannot happen.
More serious than that, if you injury or kill me in the challenge, I and my family cannot suit you. That was the ancient Chinese rule. The SC jacket is also called "hero skin". If you don't have confidence, you should not put it on.