idea
Ego is the sense of self being central to the universe, the hero of the story.
Of course this makes no sense because no-one is central to the story, the universe doesn't care about us.
Examples of ego: people discarding the risk of catching covid because god watches upon us. Clinging to a sinking ship because we think we can fix it. Ignoring an imminent danger because we think things will turn out ok in the end (covid, Trump, malnutrition)
ego death is the realization that we can't change the universe. That we can't stop cataclysms. That we are but one human in a system that does not care about us. It is recognizing the pleasures that the universe brings us in an otherwise shit situation.
grief is an enduring sensation, that something we love is going away, and we are unable to stop it. Mourning not only for the way things are, but also how they could have been.
references
Carlos Maza / How to be hopeless
Camus / La peste