Not just the mental part, but the physical part as well?
Sexual pleasure is 99% mental. When you are aroused your senses highten. Suddenly your skin and your genitalia becomes very extremely sensitive. Essentially, a lot of the systems in your body begin to behave differently. If you are not aroused then…meh. In fact, “bad sex” (when you aren’t into it) is extremely annoying.
Imagine doing CAPTCHA for eight hours a day.