At a basic level, orgasm is a nervous system response which is stimulated by extreme sexual tension. The reflex which triggers orgasm is located in the spinal nerves and the unconscious brain. The ability to hold back can come from the higher conscious mind, as when a man learns to control his speedy drive. It can also come from the unconscious brain, particularly where there is fear or sexual disgust.
Orgasm is about letting go, letting go of the mind's control over the body's actions. One of the civilizing aspects of human culture is the ability to learn not to let go; not to let the body have its clamouring way over the mind's higher desires. While self-control is essential in any group, indeed our culture would break down without it, the teaching of this control can be very overdone.