Maybe its levels. Like some people are just better at handling things then others
Maybe he is just strong-willed? People from the medical field are usually tough mentally considering they have to face deaths on a daily basis. The depression from the eggs mightbe a side-effect of him being a chicken(hen)-hybrid.
Maybe it's like the others suggested that he's mentally stronger than the others. It could also be that they could remember some general things abput their past, but something very personal, like one's own name causes them to break? Maybe a combination of both?
Yeah this makes sense to me. Poor fellow ╥﹏╥
“When they remember who they were…it breaks them…” wait then how is K okay even though he knows about his own past?