In this forum it would be how not to get the girl pregnant.
Again it's the female ovulating at the right day of the month. Add your working piece in, and the girl gets pregnant.
The only two factors is if you have a low sperm count, or
her eggs is working. It's possible her vagina canal is too hard
for sperm to swim up to it. Therefore the deeper inside
you can get the sperm to be, the more likely she will get pregnant.