The Motley Fool published a piece over the weekend about a valuation measure that has now flashed its warning signal for just the sixth time since January 1871. The previous five occasions, we're told, all ended in disaster. If your first instinct is to open your brokerage app, sit on your hands a minute first.

Valuation tools like this one, and I've written about this general neighborhood before, all say roughly the same thing: stocks cost a lot relative to what's underneath them. Fair observation about the moment we're in. It's also, by itself, close to useless as a market-timing tool.

What the doom headlines leave out is the schedule. Warning signals like this don't come with one attached. Markets that look expensive have stayed expensive, and gotten more expensive, for stretches that outlast anyone's patience sitting in cash. Selling everything the moment a signal appears has quietly cost investors dearly in past bull markets, and I've watched people do exactly that more than once since the late '80s.

My own view, and to be clear this is my read and not something a back-test promises, is that high starting valuations tend to point toward lower returns over the next decade or two. Not a crash on a Tuesday. Just skinnier returns, because you paid a high price for the earnings stream, and the math of the purchase price never sleeps.

Think of it like buying a rental property. Pay ten times the annual rent and the deal works almost no matter what happens next. Pay thirty times and you need everything to go right, for years, just to earn a normal return. The building doesn't fall down. You just bought yourself a mediocre outcome.

So what does a person actually do with a sixth signal in 156 years? The boring answer, the one I've given after every market wobble in my investing life, is that preparation beats prediction. If a decade of below-average returns would wreck your plan, your plan was too fragile to begin with. Rebalance so your stock allocation matches your actual stomach, not the one you had during a bull market.

And keep some cash or short-term bonds if a downturn would force you to sell stocks at the worst moment. That isn't fear. That's engineering.

A signal that has shown up six times in 156 years is telling you something about the long stretch ahead, not the next ten weeks. The investors who get hurt by these signals aren't the ones who note them calmly and move on. It's the ones who act in a panic, twice, buying high and selling low.

As always, I'm sharing perspective, not professional financial advice. Your situation deserves a plan, not a headline.