自分は証明する

A Rikishi proves himself by fighting. That is the only way. Through nothing else, Keiko, or so. Shoubu is the only and ultimate test.

You prove yourself by fighting the strongest opponent possible.

You can only prove yourself by fighting a stronger opponent.

One cannot prove himself by fighting an opponent who's weaker or of the same strength. It is expected that you win in such a case. Winning here doesn't prove anything.

You can only prove yourself by fighting an opponent stronger than you.

You must therefore wish for the strongest opponent possible. Only the strongest opponent possible will give you a chance to prove yourself.