I agree with Bas 100%.
Every fighter worth his salt has to believe he can beat anyone. Even when no one else believes it, he has to believe it. Self-confidence to the point of self-delusion is a common trait in elite athletes.
Ronda's "I can beat Cain" claim is a perfect example of this. I don't have a doubt in my mind that she truly believes that. You, me, Edmond, Judo Gene, her mom and everyone else knows she's got no chance, but she doesn't. She really believes it. That is the mindset that a great athlete needs to have. They have to truly believe there is nothing they cannot accomplish.