Well I’m a QA engineer, so I see both sides. Usage patterns are important, but sometimes users are just morons. When a guy walks around with a condom in his wallet for months on end, completely ignoring the package instructions that specifically said not to do that, it’s not really the condom’s fault when it fails. He put the holes in the thing. It’s the users’ choice whether they want to have a 15% failure rate or 2%. Yeah the instructions are a little bit complicated, but not nearly as complicated as raising a kid.
Isn’t one of the primary arguments for condoms is that folks in third world countries find them useful?
If the use patterns show that even educated first world people get them consistantly wrong, that’s a design flaw. Especially given the claimed market for them.
This is one thing the Billings method does well - cervical mucus is actually easier to understand.