I think it's human nature to assume that people are privy to the same amounts of knowledge that we possess, but sometimes it really is shocking to see the disparity in people's knowledge levels. Good methods of birth control just spontaneously failing is extremely rare; user error, known or not, is far more common. And sadly, sometimes people really are just not fully informed on things, even things as big as pregnancy and birth control. Hopefully this thought, while a bit depressing in some ways, will be a comfort to you in other ways -- that you are better informed and thus would be able to identify user error on your part right away, and take appropriate measures.