In the ATP's Deuce magazine John talked about how his mother supported him during his junior years living in Greensboro, North Carolina.
"My mom was the perfect tennis parent," says Isner. "She was not too demanding, but always supportive. She encouraged me to practise tennis and basketball but she never forced me into any sport." (from John Isner: The Fire Within, Deuce)Isner adds to the evidence that you do not need an overinvolved and controlling parent to be a professional tennis player. A parent can develop a good person and a good athlete.
Furthermore, I would suggest that Isner's intrinsic motivation (or fire) to compete is partially coming from the balanced support he received as a junior. He was able to develop his passion for tennis, never being forced to do something that he did not want to do.
Parents please remember this story. The next time you are upset because your child may want to take a break from a sport and you are thinking about forcing them to play, remember that intrinsic motivation or the fire does not come from someone telling you to do something. In the long run it has to come from the athlete. Ultimately, you likely are not facilitating the development of a professional tennis player but you are facilitating the development of a happy, healthy, decent adult that has passion for tennis and can use that passion to stay fit and enjoy life.