If my dog or friend or family member would die, I'd be unhappy. Understanding that death is natural wouldn't do much to that unhappiness. Maybe someday I'd get over it, or maybe not, but either way, it wouldn't be because I gained some deeper understanding of life and death.

> it doesn't make you unhappy if a wild animal attacks you when go into its cage

Maybe we have different definitions of unhappiness at play here, because being attacked by an animal would definitely make me unhappy. I mean at the moment it would mostly make me fear for my life, but afterward when dealing with the damages I got, I think I would be quite unhappy, and understanding that really I'm the one to blame wouldn't help. It could make me more unhappy, leaving me kicking myself for doing something so stupid.

I wouldn't blame the animal if that's what you mean, but that's different from happiness/unhappiness.

> are you upset because you can't fly like a bird

I think that's more because my hopes and dreams are shaped by the environment that I've grown up in and, living amongst other humans that can't fly like a bird, the possibility of doing that has never occurred to me, at least not for seriously enough to become an issue of happiness.

Had I been a born an elephant with huge ears that all my so-called elephant friends would torment me for... yeah it would make me pretty unhappy if those ears wouldn't at least give me the ability to fly.