In a study of 18,000 NBA games, teams behind by 1 point at halftime won more often than teams that were ahead by 1 point. Another study done through a typing competition found that those told that they were slightly behind in the competition performed much better after the feedback.
Positive feedback feels good. Being ahead in the race feels good. Yet, it seems that we always have more to give. Knowing that we have room to grow can be a great motivator. Since most of us aren't in the NBA or engaged in typing competitions, we need to define what we are slightly behind in.
Know that you might be great, but you haven't arrived yet. You can do better. Knowing that you have more to give can be what it takes for you to go from good to better.