Well, I'll probably lose all credibility by posting this, as it sounds so wacky.
Some days I get better results with my sharpening steel than others.
Often it seems like nothing's happening -- I can swipe it for 2 minutes and it's just not doing anything to the edge. Then another day, whoa! a few strokes and the knife is noticeably sharper.
Could there be something atmospheric going on? Is that too far-fetched an idea? I only have one sharpening "technique," so I don't think that's it.