Is it the size of the boat?

I reckon both! to be truthful i also think it depends on the woman! if you're fucking some whore thats loose with a very very big dick, she wont feel it no matter how good your humping.
All i can say is, play around get the girl close to climaxing before you shove your winky in, then you feel powerful :D thats what i learnt in my teenage years! i always lasted long because i was drunk