Going in one more round when you don't think you can. That's what makes all the difference in your life.
Rocky is revered for his ability to absorb more punches than anyone else. He is impossible to knock down. His way of approaching boxing mirrors his way of approaching life; his life has not been easy but he continues to persevere. He believes that as a boxer, and as a human being, what can separate him from other people is willingness to get up again every time he is knocked down and that eventually he will be the only person who gets back up again.
Every champion was once a contender who never gave up.
This is another of the motivational mantras that Rocky lives by. He believes that tenacity and never giving up will eventually triumph. He knows that very few people start off by being a champion, or a superstar. They were not born invincible. Their success has depended upon their getting up time after time after time until eventually they prevail. Rocky is using this theory as inspiration for his own perseverance and he knows that although he might lose the fight this time eventually he will be the champion also.