MRI scans taken while participants were masturbating reveal what happens to your brain at the moment of orgasm:
"Over 30 areas of my brain are activated as I move from start to finish, including those involved in touch, memory, reward and even pain. As [researcher Barry] Komisaruk expected, the imagined clitoral touches and Kegel exercises activated the same brain areas as real ones, albeit with somewhat less blood flow.
The [prefrontal cortex], however, showed more activation when touches and pelvic squeezes were imagined compared with those that were real. He suggests this heightened activation may reflect imagination or fantasy, or perhaps some cognitive process that helps manage so called "top-down" control - the direct regulation by the brain of physiological functions - of our own pleasure."
Maybe this explains the "thinking off" phenomenon - just thinking about stimulating your clitoris and squeezing your pc muscle lights up your prefrontal cortex. Could some women have difficulty achieving orgasm because they can't stop thinking about life and start thinking about sex? It's a strong argument considering this research.
The ability to fantasize is so important.