The definition of stupidity is doing the same thing over and over again and expecting a different result.
Isn't that what a writer does every time we submit a story or send a query to an agent?
Except it's never exactly the same: it's a different story, a different editor, a different agent ... a work written weeks, months or even years after the last, and in that sense, written by a slightly different writer, too. Maybe we're working through a particular theme or writerly habit; maybe our lives have taken a recent turn; or maybe we're simply in a different mood.
Sometimes, I worry that my skill is not improving, that I'm only getting worse - losing the spontaneity and picking up artificial affectations in exchange. It's tempting to measure this by ratios, acceptances, manuscript requests, but nothing happens in a vacuum: the agent might be looking for something in particular, the market just accepted another story about time-traveling opera cows, or someone on the other end was simply in a bad mood.
Lack of success doesn't mean lack (or loss) of skill. But how do you know what does? Or does it even matter? Maybe you at your worst is just what some editor wants.