The pursuit of perfection
The law of diminishing returns: more and more gets you less and less. It's familiar in many domains: economics, martial arts training, propulsion. Rush Limbaugh would probably agree it even applies to drug use. It certainly applies to developing software. There's only a certain value derived from polishing a chunk of code. So, while I'll reserve opinion about whether this is a 'law' of nature, it's definitely something we observe in many contexts.
It's interesting to me to note where the law of diminishing returns appears to break down.
I have always been intrigued by one of the ad lines used by Lexus: the relentless pursuit of perfection. For me, perfection is spelled Porsche, but I like that Lexus boldly puts perfection as the aim. The idea of pursuing perfection seems to be thumbing one's nose at the ol' law of diminishing returns.
While we're not all engrossed in engineering the ultimate automobile, I think human artistic endeavor in general doesn't pay much heed to the law of dimishing returns. I imagine an artist relies more on a sense of holistic completeness when deciding to stop working on a piece. Education is another area. Imagine telling your boss, "Er, I think learning more about this is just pushing the law of diminishing returns."
In the end, it may be that the law of dimishing returns governs all our activities, but intriguing to me is how our perception influences our efforts. In the pursuit of perfection, I think we perceive each additional effort as adding value. We don't see that value dimishing or we would likely give up. So, despite the 'law' of diminishing returns, it may be our perception that makes the difference between accomplishing something mediocre and something great.