This is an important point. The failure rate measures, "If 100 people otherwise capable of becoming pregnant have an average amount of otherwise potentially pro

This is an important point. The failure rate measures, "If 100 people otherwise capable of becoming pregnant have an average amount of otherwise potentially procreative sex for a year, how many of them will get pregnant?" Nine out of every hundred is a LOT to start out with. And if the "average amount of otherwise potentially procreative sex" part increases by, say, 11%, you get one new pregnancy out of every hundred.