Competitiveness is a requirement for becoming a successful tennis player. It is the basis for the motivation to work hard to improve skill and compete to win.
Being competitive means players also feel the emotions of competing more strongly. Competitive players feel more joy and relief when they win. But they also feel more fear and frustration to do with not winning.
This in turn makes them more vulnerable to developing unintentional habits that are about avoiding and reducing the fear, frustration, and pain that comes with possible and actual loss.
If players are to become successful a high level of competitiveness is required. But once this is present the next most important focus should be for parents and coaches to help these players learn how to respond well to the more intense difficult emotions to do with competing that they will naturally feel.