This is laughably false.

https://www.timeshighereducation.com/news/life-span-of-human...

I was merely expecting a “this is false because of X”. Rather than “this is false”

I guess we all have our biases.

People were commenting that the idea that every cell is replaced in a living organism is 'laughable'. Brain cells and osteocytes were cited as examples of cells that are never replaced.

However, I still think, and more strongly than ever, that brain cells and osteocytes can be examples of unchanging cells if an only if it is proven beyond a shadow of doubt that every single atom constituting such cells remains intact during the lifetime of such cells.

Since the human body is subjected to a lot of physical stress and damage and repair is continuous, it is possible that damaged brain cells or osteocytes get replaced with new ones. Need to read more about this, though.

Adult neurogenesis or brain plasticity is a fact. Skin cells, blood cells and all types of cells have a finite lifespan - a few days to a few months.

Osteocytes in human bone can live up to 50 years.

"New neurons are made in just two parts of the brain—the hippocampus, involved in memory and navigation, and the olfactory bulb, involved in smell (and even then only until 18 months of age). Aside from that, your neurons are as old as you are and will last you for the rest of your life. They don’t divide, and there’s no turnover."

But while it applies to many cells over varied lengths of time (up to many years), it doesn't apply to all cells.

https://www.livescience.com/33179-does-human-body-replace-ce...

https://www.snopes.com/fact-check/does-body-replace-itself-s...

So the idea does apply but not exactly as you claim and it's definitely not absolute, even for atoms, let alone cells.