uh yeah it doesn't work because everyone has sex eventually. In that respect it has a 100% failure rate. Unless you are a monk or a nun and even then, how do you know for sure? Most people using this end up in a situation that is out of their control...i.e. oh whoops! We weren't going to have sex but whoops we did. Oh whoops, look I'm pregnant. Or oh whoops guess I married a loser and didn't know it because we never had sex before we got married. What a nightmare.
