Imagine you are a woman. Your partner asks you to masturbate him to orgasm. Each time you do this, you would notice that the length of time varies. The amount of stimulation required differs. This is because a man’s initial state of arousal varies and his engagement in the activity (thoughts in his head) vary from occasion to occasion. Imagine if you said that when masturbating him, you will only offer this stimulation for a set period of time determined by you that has nothing to do with how long he needs the stimulation to last for. He wouldn’t be very happy, would he? Stimulation must continue until orgasm is reached. Likewise, a woman cannot determine how long intercourse will last. Consequently, a woman cannot orgasm from intercourse regardless of the anatomy assumed to be involved.
Stimulation can be physical or psychological. We can be stimulated physically by doing something and we can be stimulated psychologically by thinking about the same thing. For example, we can compare our enjoyment of eating a meal with the enjoyment of thinking about eating a meal.
Men may think that arousal is the period of time when they obtain physical stimulation with a partner or through masturbation. But arousal occurs before we contemplate physical stimulation. This is because genital stimulation is only effective (likely to lead to orgasm) once we are mentally aroused (when men have an erection and responsive women use fantasy).
Women refer to fantasy as if it is optional. Some women say their fantasies involve emotional situations such as an affair, swinging or a loving relationship. But these are social situations for a woman. They are also based almost wholly on intercourse. My conclusion is that orgasm is an instinctive response that arises when our minds are focused on explicit eroticism.
There are graduations in arousal from stone cold to the instant before orgasm occurs. But in the early stages, we may be a long way off achieving orgasm (except younger men and boys). As adults we may need an appropriate situation or a relaxed mind and an opportunity for privacy before we can focus our minds on obtaining both the mental stimulus and the physical stimulation that we know (from experience) are a requirement of orgasm. [i]
In the context of achieving orgasm, erotic stimuli have to be more than a short skirt or a cleavage. In order to reach orgasm, a man needs to focus on an image or concept that relates to explicit penetrative sexual activity. I have found that my fantasies that I use to achieve orgasm also have to be extremely explicit and focus on conceptual aspects of penetrative sex.
[i] It would also seem as if there is a definite break between sensuality (diffuse, non-focused physical feeling), and sexuality (drive toward orgasm), and that in order to have an orgasm, at least most of the time, it is necessary to think and work and concentrate toward one. (Shere Hite)
Excerpt from Understanding Sexual Response (ISBN 978-0956-894762)