I'd assume that to be true for various reasons such as: Penis can't get erect (blindfold and nose peg for the guy could fix that though) Even erect, penis can't reach past his fupa and hers Guy has sex with the wrong damp fold Sperm stop for snacks on the way or are too lazy to swim that far, demands that the egg come to them are unanswered. I'm making myself feel sick now so I'm going to stop.....