I've had a few appointments where I couldn't finish, usually there was something about the visit that put me off my stroke or left me feeling a little disappointed or even cheated. Expecting a threesome and it being cancelled last minute certainly could put me of my game.
But I've had some very good appointments where I didn't finish. The most memorable was a lady that advertised natural breasts that turned out to have a terrible boob job. Personally I have issues about unnecessary surgery and I found this a real turnoff. But otherwise she was a wonderful girl and extremely enthusiastic and I actually extended the appointment but never crossed the finish line. Had to visit another lady to finish the job.
No little blue pill though. My only experience with Viagra was when some "friends" spiked my food. That was when I was at an age that I definitely didn't need any help in that department. Gave me an insatiable hard-on that lasted 5 hours. Luckily, I had 2 medical students that took very good care of me.