Is this a plothole? Question about the Endless

[Carin-Eri]

I think the endless are supposed to be based on the happiest memories of the person or the happiest version of themselves. If that’s true, then they must be able to distinguish between the good and bad memories contained in the aether.

That's quite tragic in a sense, if you look into it a little more deeply. Some of those Endless were children. This implies that those Endless either died AS children or had miserable adult lives and their only happy memories were those from when they were children.