Yes, I know that we've all seen the "bad actors" on the court, but there is little question that, when one learns to play properly, and with the right coach, self-discipline is a great end result. Tennis requires you to work on improving your skills during practice and to control the pace of play during competition, which builds discipline.
Although research has shown that self-discipline in human beings is limited and that we are really creatures of habit, tennis can certainly help improve the habits surrounding your self-discipline. In tennis singles, you are by yourself on the court, making decisions on your own, planning strategies on your own, and truly developing your innate skills of self-discipline.
In 1996, Yoo examined self-confidence and competition anxiety among various sport activities. Tennis was among the sports examined to study several psychological factors. Yoo found that the higher the sport orientation, the less competition anxiety and the more self-confidence.
In another investigation of wheelchair tennis participants, Greenwood compared wheelchair tennis players to wheelchair non-tennis participants. It was determined that wheelchair-mobile people participating in tennis seem to be more confident about general wheelchair mobility tasks than are wheelchair-mobile nonparticipants.