As ThePixie mentioned, I think the moon should probably be taken into consideration too when relying on natural methods. I was thinking of the moon when Raven said she didnt know how it happened. A gp I used to have said she has seen numerous woman concieve at times of the month differing from what their charts said should have been possible, and she believes the moon has something to answer for that too.

Me and DH have always used charting throughout our relationship, to concieve and to not!
We use condoms or dont dtd at times when we think a pregnancy is likely. However in 9 yrs, we have had one ooopsie, which I sadly lost. According to my chart we dtd a full 5 days before I ovulated. But my fertility teacher and Gp I saw at time of getting the posistive test had said that a week either side of Ovualtion can result in pregnancy, we just didnt the chances of it were very likely.