A long day, but a good day

I learned to day that discussions about gender are very different at a nonprofit that is overwhelminly female than they are at an engineering school (even one that is almost gender balanced). One woman mentioned that men tend to make proclamations while women make more tentative statements. This reminded me of the resume/cover letter thing, so I told her about this, and about how even though I know it's not in my best interest to write humble cover letters, I can't help doing it. But she surprised me by saying not to abandon this style, because when she's reading cover letters and she sees a 22-year-old making overly confident statements about how they *will* be an asset to the company, she gives that letter a "pssh yeah right" and moves on to the next one. So now I'm just lost... how am I supposed to write an effective cover letter unless I know who is going to read it?