birth control and condoms are 100% but they cant sell it with those odds.
people are stupid and misuse things, and would later try to blame the product.
and some people are simply immune to the hormone birth control drugs. its far less then 3 out of 1000 that are, but they wont take chances.
why do you think every product is 99% effective? its 100. its stupid people that they cant prove used it wrong.