This is efficacious, though - it's just not as effective as other methods. For about a decade, my wife and I were fine with the lower effectiveness of the rhyt

This is efficacious, though - it's just not as effective as other methods. For about a decade, my wife and I were fine with the lower effectiveness of the rhythm method. We were smart about it and had no issues, but if she'd gotten pregnant during that time it wouldn't have been a huge problem. In our case we based it on the date of menstruation, and giving enough of a buffer to feel comfortable. It worked. We've had two children, both of which were planned, and both of which were conceived within a month of our decision to do so. Like most things, it's a tradeoff. We didn't want to have a child at that particular moment, but weren't willing to completely abstain to ensure that. It didn't make sense for us to use condoms, oral contraception, or an IUD at the time either for various reasons. We were willing to accept the risk, so it wasn't a problem.