The following is the Tale of Kassandra from Assassin’s Creed: Odyssey.
Over 2000 years ago in Ancient Greece, there was a formidable, mercenary warrior named Kassandra. She was the descendant of Great Leonidas. On her journey to reunite with her family after years, she discovers her real father is none other than Pythagoras, the great Greek mathematician. But eventually, Kassandra learns that Pythagoras is the secretive leader of the Cult of Kosmos, a cult that is corrupted, with evil intents. Kassandra has to fight and kill her own father, and from him, she acquires The Staff of Hermes Trimegistus. This staff strengthens Kassandra, disabling her ability to age or deal with wounds, it sharpens her instincts, her combat skills, her physical conditions. She becomes immortal, and she is soon contacted by figures she could see and hear but not touch and feel. They inform her that she’s the chosen one, chosen to walk the Earth for thousands of years and secure other magical artifacts like The Staff of Hermes Trimegistus and stop them from falling into the hands of evil organizations, like The Cult of Kosmos. At first, Kassandra enjoyed this immortality, nothing could harm her, she was the strongest being on Earth, but soon, it felt more like a curse than a blessing. Kassandra saw the rise and fall of empires, saw her loved ones perish, even outlived her own descendants, her own grandchildren. Kassandra walked among many other Greek Gods in her time and continued to serve this duty given to her of securing the artifacts.
In the end, immortality becomes the worst curse one can have, walking the Earth you have explored for thousands of years becomes boring, depressing, gaining all the knowledge in the world and having nothing more to study becomes pointless. It’s the equivalent of being locked in a room and nothing to do in there, only the world is that room for people cursed with immortality.