First it's his new car, then it becomes his new car with new tires, and then his car with new windshield wipers, and finally his old car with all new parts and some old ones. None of them are the same car.
I think in cases where it' a major rebuild, like turning a WW2 Minesweeper first into a ferry, and finally into Cousteau's research ship Calypso this outlook is more obvious. Are these ships all the same despite getting almost a full refit at each stage? I would say none of them are the same ship, but completely separate "things" with some old and some new parts.
What if you disassemble all of the car except the wheels and reassemble it but with new wheels?
How about if you also exclude the seats too.
At what point does the answer change? That’s the whole point of the ship of theseus.
More relevantly, I don't think neurons are replaced. There must be some material churn in the atoms and molecules that make them up, but even then different for different molecules - e.g. I don't know how much of our DNA molecules get replaced over a lifespan from the repair or other mechanisms.
Tattoos however, IIUC, sort of "float" between cells, and as those cells are replaced one-by-one the ink is kept in place by the surrounding cells that are still there.
Answered by Kurzgesagt: https://www.youtube.com/watch?v=nGggU-Cxhv0
