It’s called the Theseus Paradox.

According to Plutarch, there’s an Ancient Greek story about a 30-oar ship belonging to King Theseus, which by standards of the day, was extremely old.

The reason it lasted so long was because over the years, every time one of its wooden planks, an oar, a mast etc. got a bit worse for wear, the dutiful crew would replace the part individually with a new one.

Of course, do this for long enough, and it’s just a matter of time before all the parts of the ship have been replaced at least once.

Which begs the question, at this point, is it still the same ship?

And if it’s not the same ship, at what point did it stop being the same ship? When fifty percent of the parts had been replaced? Eighty? Twenty? Five? Who decides? By what criteria?

Presumably, fans of Notre Dame would’ve asked themselves the same question, when they recently rebuilt the cathedral after the terrible 2019 fire. Is it still the same church, or did we end up building a new one? 

Or take the human body. On average, our cells are replaced every 7-10 years. Some cells last a few days, some last a lifetime. But when does the old body become the new body? Is it actually new?

Millennia later, the paradox remains unsolved. 

Funnily, one group of people who face this paradox on an ongoing basis are leaders. Employee turnover is a thing, so is replacing warfighters.

How do you replace people without changing the core culture?

The answer is actually in the question. 

Take the US Marine Corp. Every few years, they may replace nearly every Marine. New faces, new bodies, new minds. Yet, somehow the Esprit-De-Coeur changes relatively little. Why? Because they have a code. An ethos. A set of rules. A discipline. A way of behaving that everybody is expected to maintain. And they’ve had it for a while, forged in places like Tripoli, Iwo Jima, and Parris Island.

A culture.

The culture is so resilient because everybody knows what it is. From the lowest Private to a Four-Star General. Everyone knows, everything is reinforced at all levels, everyone is aligned. They don't protect the planks. They protect the idea.

Theseus would be proud.

Your organization is always replacing parts. People come and go. Processes change. Products evolve. What's the thing that doesn’t change?  
If you can't answer that, you might not have a culture.

Maybe that should change?