Asklemmy

Without getting into the heat death of the universe and all that, I can think of something that happens much, much sooner. I'm only middle aged and I already don't like where the world is going. Can you imagine being centuries, or eons past the era you identified with? Can you imagine how insufferable young people and old people alike would seem when you have centuries worth of life experience and wisdom? Can you imagine a horde of little edge lords on the internet confidently yet incorrectly telling you about the signing of the Declaration of Independence, when you were there when it was signed?

Having to constantly find new hiding places for the blood chalice, and keeping up with all the latest scanning methods so you can develop countermeasures. Your secret is never truly safe.

Having to keep track of that evil snail.

https://www.reddit.com/r/AskReddit/comments/5ipinn/you_and_a_super_intelligent_snail_both_get_1/

If other people are also immortal, the awkwardness of all of them eventually becoming your exes

I don’t think you’d remember a break up from hundreds of years ago, let alone be upset about it.

Idk id be super depressed if I was able to experience my family, friends, family's children, and so on die.

The Sun will eventually fry all life on Earth and boil off the water & atmosphere. Eventually the Sun will die out completely, leaving you on a cold, dark rock.

LoL investing and compounding! I literally have all the time in the world.

The eventual heat death of the universe would be painful

i think that experiencing all the things & people i care about would be the worst of it.

either that or seeing us repeat history over and over again as a society complete with all of the indifferent cruelties it entails and studying it, but ignoring it anyways

I'll say no one can truly know. Unless you are yourself immortal

Boredom after some period of time, you will have some everything there is to do.

One of my books features an immortal protagonist and I've as such thought about this quite a bit. More than the answers already provided here, what I found interesting as a writer was the balance I needed to find between making an immortal detached from mortal values while still being engaging to mortal readers.

Said as a pithy question, if you can outlive everyone's decisions and mistakes, what would it take to make you do anything at all?

Government Bureaucracy.

Renewing a driver's licence or passport. The individual looking at your application will see the date of birth and raise a red flag.

Getting imprisoned for thousands of years unable to get out.

As we get older, our perception of time speeds up. An immortal would easily lose track of time after just two human lifetimes, causing an immortal to suffer from dementia-like symptoms where they expect one date but find themselves habitually late. And since time doesn't mean the same thing as us to an immortal, they would eventually become disconnected from the world around them and be unable to reintegrate. They wouldn't be able to maintain friendships, relationships, mortgages, payments, etc. They would be surrounded by people but forever alone.

Being eaten by sea anemones, tuna, sharks, swordfish, sea turtles, penguins, and other jellyfish.

https://en.wikipedia.org/wiki/Turritopsis_dohrnii#Predation

Based on your question, you might dig the book “Boat of a Million Years.” The author put quite a bit of thought into just that.

https://en.m.wikipedia.org/wiki/The_Boat_of_a_Million_Years

Just depression in general. I don't want to live one lifetime, let alone never being able to die.

If you're immortal in a body that isn't broken then that might be a different story, but you'd still grow to love people only to have to lose them and go through that pain over and over.

Everyone else in your life that isn't immoral (if you're the only one who is) dies eventually, so every time you make a friend or start a family, you do so knowing that you will have to watch them all die someday.

Not being able to kill yourself.