Heard that before. And there is much truth in it. But running out of ammunition is not possible, people do miss (for various reasons) their intended target, and more than enough bullets beats not enough bullets.
Some people act like there is nothing that can prevent them from taking out a target with 8 rounds of .45. I can think of several things: certain kinds of barriers, operator errors (unless of course, both you and your 1911 are absolutely infallible, along with that one-shot stop super bullet you are using...don't worry, we believe you), getting shot or otherwise injured during the engagement, the introduction of extra targets that weren't there before, etc.
Having said that, more bullets doesn't guarantee a winning situation. Just more opportunities. And no, I'm not saying drop that 1911 and run out to get that 17+1 9mm. If you're carrying that 8 rd 1911....just carry a another mag or two...or more. Same with anything else....you can never have too many bullets. Too many is just enough. Just enough....is never enough. Ya never know.