Some people work hard and keep on working, but no play. They do well for the short-term or sometimes mid-term. However, they eventually burn out and lose their steam because there is no reward or celebration.
Some play hard and keep on playing. They are fun-loving and nice to be around. However, they are unable to sustain this because eventually their resources run out.
The goal of working hard and playing hard is a good balance. This provides you with the energy to keep going because you get a chance to replenish your energy and also create resources to sustain your play.