This question is for both the gals and the guys.
Is one orgasm enough for you?
I think of it this way... what if you're watching porn and extremely turned-on... masturbating... isn't it a little annoying to only cum once? Because when you're watching porn, there is SO MUCH to enjoy! A whole movie's worth!
Or when you're having sex and you're partner looks really hot and you just want to fuck them all night... cumming once just isn't enough!
I actually feel bad for guys, 'cuz once they cum, they go limp. Of course, if they're into anal, they could always stimulate themselves that way, which I know first-hand can feel really good to a guy. I also feel bad for me when I'm with a guy, 'cuz getting a mouthful of cum or a load in my ass feels so fucking good that I don't want just one!
But, these are only a few ideas/possibilities... feel free to ramble about it!