A creature can not live with this realization not supressed. You cant take credit. You cant have a loved one go on a journey alone. If you where fully aware of you mortality, you would cower in a bonker like a nomad crab in its shell. Maybe one would storm outside from time to act in fits of panic.

And yes, those edgy adults, claiming to be aware of death/mortality and accpeting, usually have created lightning rods in theire conciousness for these fears.

Like believe systems, that reroute this fear into believe of immortality, or in the atheist case a feeling of superiority for living your life to the max, while all those others do not. Those fully aware are in asylums