The Motley Fool published a piece this week claiming Warren Buffett has followed a single investing rule for decades, and that history shows he's never been wrong following it. You can read it here.

According to the Fool's telling, the rule is the famous one about being greedy when others are fearful and fearful when others are greedy. Buy when the crowd is running for the exits. Trim when the crowd is partying. It is one of the most quoted lines in investing and among the least followed, though I'd confess nobody has kept an official tally of either. The article doesn't quote Buffett directly on it, I'd note, but the sentiment is unmistakably his and has been for a very long time.

The Fool's framing, that he's "never been wrong," is doing some heavy lifting. Buffett has publicly acknowledged mistakes over the years, and a six-decade career without them would be the real news. What the article really means is that the discipline has held up over time, and that part I'll grant. Buying quality businesses when nobody wants them has worked in every cycle I can remember, and my memory reaches back to the crash of 1987.

But think about what the rule actually asks of you, because it is easier to admire than to execute. Say you had bought an S&P 500 index fund in March 2009, right at the moment of maximum fear, when your neighbor was swearing off stocks forever. That turned out to be one of the great entry points of the modern era. Say instead you waited until the panic subsided and things felt safe again, a year or so later. You still did fine. The gap between those outcomes, though real, is smaller than the gap between investing and sitting in cash waiting for certainty that never arrives. The rule isn't really about catching the bottom. It is about not letting fear make your decisions for you.

The headline writers skip that part. Being greedy when others are fearful requires you to buy things that are falling, in public, with your own money, while everyone around you explains why this time is different. In the worst stretches of 2008, I suspect it felt to most people less like an opportunity and more like catching a falling knife in a dark room. Steady, small purchases during a panic take a kind of courage that has nothing to do with math.

And the fearful-when-greedy half matters just as much right now. I've written in this column before that I believe the S&P 500's valuation is stretched near dot-com territory, and that's my own read of the numbers rather than a settled fact. Either way, trimming or holding cash when prices feel rich is the same rule, pointed the other direction. It's the half nobody puts on a T-shirt, because selling into strength feels like leaving the party early, and nobody wants to be the person at the door while the music's still playing.

So the Fool is mostly right, with an asterisk. The rule works, in my view and in the historical record the article points to. The man applying it was imperfect, which is actually the encouraging part, because it means you don't need to be perfect either. You need patience and consistency, and a willingness to keep buying good, boring things when your stomach votes no.

As always, this is my perspective, not professional financial advice. But if you take one rule from Buffett, take that one. It's held up longer than most of us have been investing.