Imagine you keep flipping 10 coins, stopping each once it has come up heads. Eventually all will have come up heads. But if you do this a bunch of times and kee

Imagine you keep flipping 10 coins, stopping each once it has come up heads. Eventually all will have come up heads. But if you do this a bunch of times and keep track of how many times you flipped the last coin, there will be a certain number of flips at which the end is most commonly reached. The "mortality rate" increasing then flattening out is just this curve reaching its peak then declining. The math of this is easy enough to figure out so not sure why there is a mystery amongst biologists about it.