Eternity
I like the thought of eternity.
Eternity promises many things that would otherwise be untrue. Stability, predictability, the lack of the unknown.
Eternity isn't promised to anyone though. Lives end, relationships change, identity changes.
Change hurts. It's scary and unpleasant and most of all, it's unknown.
Eternity would be nice. We don't have it though. Instead, we're left in a constant state of change. It's scary and painful, but it's what we have. It's why humans adapt to accept and understand change.