Because it's been around so long, it's the one thing that most people have heard of. Your grandma, mom, cousin, aunt, pastor's wife and the gal at the grocery store have all heard of it - even doctors and nurses - and for whatever reason it's taken on a life of its own and no one ever gets the message that it has been TOTALLY debunked. We know exactly what Shettles did wrong, the mistake that he made, and yet we still can't get rid of timing. I think a lot of people hear "timing sways" and then in their minds they turn that into "well since I got a boy that means I must have gotten pg at ovulation" even tho they actually DTD 2 times before ovulation and just forgot about those.