Men learn to fear penetration. This occurs sometimes as the result of unfortunate experiences, or unusual ideas about the effect of penetration. Less often it occurs because of fear of causing pregnancy, or acquiring a sexually transmitted disease, or uncertainty about sex itself.
Early sex accompanied by guilt, pain or discomfort, can lead to fear and avoidance. Sexual drive is not affected by this fear. The longer a man fears, the more skilled he gets at justifying his beliefs and he will take another path, for example masturbation.
A therapist will help a man identify his fear and help him work out the evidence for it. The man will then be offered a choice of working alone or with his partner in therapy at ways of overcoming his fear so that he may penetrate when and as he wishes.