- A successful surgery may require both a surgeon and a nurse, but that doesn't mean the nurse has nearly as much impact on the successful surgery as the surgeo

- A successful surgery may require both a surgeon and a nurse, but that doesn't mean the nurse has nearly as much impact on the successful surgery as the surgeon. - The lighting of the match is mainly caused by the striking of the match, not by the presence of oxygen, even though both are necessary for lighting the match. So a cause being necessary for an effect doesn't imply that its impact on the effect is very large.