Given a long enough time frame, the vast majority of an immortal life would be spent buried beneath something or floating in the void of space. Think about it, you outlast planets and stars. When those go dark, but you don't die...nothing to do but float in space.

You might counter that with, "well yeah, but eventually I'd find other sentient life forms and/or people again.” And sure, maybe, but that wouldn't last as long as you...and then you're just alone floating in space again, for the vast majority of your life. The only thing to look forward to, since you will outlast everything, is the end of time itself.

The disappointment of experience winning lifetime supply of something but that would eventually turn into a lie

Nobody is answering the prompt lol. Everyone says all of this shit all the time.

You live long enough to never feel at home. Sure the loneliness sucks or whatever, but who do you root for at the football game?

Having to buy new shoes for the rest of eternity. You know how much work I've literally just put into finding shoes that 1) don't suck and 2) aren't made with slave labor? It's impossible. Drives me insane. I'd found my own shoe company once I become immortal rich just to fix that problem alone. Maybe other stuff too we'll get there

I suppose on that note: it seems like a really bad idea to become a public figure after a while. Like you obviously don't want your immortality found out. You have to have like illuminati power before that point though, but it could happen at any time. Like if something happens and you become a news item (i.e. helping someone out and a video goes viral online). Not saying everyone is all that close to going viral, but over a sufficiently long lifespan you're effectively rolling that dice a lot.

If we're talking magical immortality, as in you can't die, at all. Then the fact that however much enjoyment and experiences you get while the universe still exist, it will be followed by an infinite stretch of nothing after the heat death of the universe.

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.

I suppose it depends on the rules of this specfic immortality. As someone who lives with chronic pain that literally never feels physically comfortable in any position, immortality sounds like a cruel joke. Not that I'm suicidal or eager to die, but the fact that it would progressively get worse and worse without any sort of end is.... horrorific.

Time gets shorter. I've already experienced this going from my teens to my twenties and into my thirties. I can remember entire weeks of my childhood. By the time I was in my mid twenties, days and weeks blurred together. Now it's like months go by and I don't even notice.

People talk about it more as they get older. Eventually when you enter your 80s and 90s, it's like entire decades can come and go. So imagine when you're immortal. If you've been alive for 100,000 years, that's longer than writing has been around. Entire civilizations will have come and went.

But from your perspective, it's all a blur. Entire genealogies were experienced, yet those people barely registered in your mind. If you had a favorite food, maybe the recipe disappears when you went four centuries without eating it. Jokes and fashions you're familiar with are completely alien to everyone else. Are you even capable of noticing when things change at that point?

There's also the question of how human are you? Everything and everyone would seem inconsequential. Would you even be able to socialize with others, or would you be completely sociopathic? That's if you don't hurt anyone and get tossed in a jail cell. What happens if you spend a few centuries in prison? Fight in multiple wars? Would you even feel the slightest discomfort when you kill someone?

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.

A lot of ways to die are excruciatingly painful, but you die, so you don't live with the pain. If you end up in one of those situations and don't die (because you are immortal), I imagine the psychological impact of the pain without immediate release could be enough to completely break you, mentally.

Having to listen to that Queen song, forever.

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?

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

You know how the curse of pet ownership is that you will almost certainly outlive them?

That, but with everyone you love

The eventual heat death of the universe would be painful

If you're injured and you survive with the scarring from said injuries. Well, good luck because you're now going to wear those and wish you had died from them. If you're incapacitated or amputated? Gotta live with that for years and years.

Forgetfulness. Think how forgetful people get after having lived a normal lifespan, now go for a few thousand+ years and you’ve probably forgotten whole centuries of your life. This is actually the premise of a solo journaling game Thousand Year Old Vampire, you have to cross out and forget memories as you progress through the game, just forgetting whole parts of your life.

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.

Family meals that take 3 restaurants No retirement

I wonder if it might engender an advanced sort of solipsism and callousness towards other people. After thousands of years of the world coming and going around you while you remain, would you even recognize other people as real or meaningful?

outlasting humanity and all its trappings

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/

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.

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.

Btw if you were actually immortal, after a while you would just go into shock and enter a vegetative state from all the psychological stress.

If the ultra rich find you out, you can expect lab-rat life, at least until all modern systems collapse. Death is the only thing those suckers fear, because regardless of their net worth, it comes for all, even if late. They would do anything to find out your trick