Why is it?

Why is it that if a woman gets pregnant whilst using NFP, people use that as "proof" that NFP doesn't work, but if a woman gets pregnant using hormonal birth control or condoms or whatnot, it's seen as a fluke?  Nothing, barring complete abstinence, is 100% effective at avoiding pregnancy.  Sure, some methods might have less wiggle room, so if a couple doesn't practise it correctly, they're more likely to conceive with some methods than with others.  That doesn't make the method unreliable when the couple are not correctly practising that method.  And sometimes pregnancy is going to occur even if a couple is following a method correctly because, again, nothing short of absolute abstinence is 100% effective.  Sorry, this is just a pet peeve of mine.