It is said that the persons who "invented" sex therapy, have said that we can assume that persons with sexual problems are more occupied with their own sexual behaviours and thereby less attentive to their own sexual feelings.
This behaviour is called "spectatoring", which means that the person see oneself from the outside.
People enter this "spectatoring-role" when they feel nervous and uncertain of things in the sexual area, e.g.: "if she at least could enjoy it" or "last time she didn´t come either".
These thoughts are often not so exciting and create expectations and requirements on the sexual act.
In sex therapy the therapist focus on allowing the patient to control these thoughts.
If pain arises in the vagina or an erection problem occurs during the intercourse, it often leads to a terminated intercourse.
One goal with sex therapy is to teach the person to enjoy having sex, without any problems to get sexual aroused and without negative thoughts.
Sex therapy alone might not always work. There may be specific problems that demands special help and therapy, eg. relationship problems, that could be solved with relationship therapy.
Another goal with sex therapy is to reduce the demands that people must have on sex, the demands that we need to learn and know our own and the partner's body, and the demand knowing what we like and how both partners would like to have the sexual act.