Mr. Popo, Krillin and others in “Unfinished Business”

To be truly strong, you must know yourself and your enemy. Once you know this, all will become clear.

Krillin

What do ya mean? Know myself?

Yamcha

Don't give us that rubbish! How could we not know ourselves?! I know myself better than anybody!

Oh, is that a fact? So you know yourself, do you? How come you don't know that you are weak?

Yamcha

Whoah! Would you like to prove that!? You beach ball!