It is chemistry and physics. If the chemistry was great, physics will happen protected or unprotected (especially when enough blood isn't pumping into brain because all blood was pumping into our dicks). It happened me very recently. We were both got very horny, girl was dripping wet. Initial arrangement was 50% play, 50% massage option 4. I always start with fun bit then massage. Ended up with a BBFS, she wanted it. There was no massage. She never asked for anymore $. Fun was mutual