There may be days that Serena Williams does not feel like training. It's been 30 years of feeling like an underdog, being sore and working hard to get to and stay on top. But, there are no days she feels like losing. She knows there are athletes out there with posters of her on their walls, dreaming of the day they will be better than she is. While wearing Nike gear, the tennis powerhouse works hard on her game, highlighting the fact that one reason for her athletic success is her unlimited willpower.