Either “Boredom: After some time you have seen basically everything.” or “Can’t keep up: The world changes so fast, and I’m, stuck in a mindset I acquired in 1543”.

And: Bureaucratic nightmare. “We have you on file as being born in 1924, but you don’t really look like a centennial. Can I see your passport instead of that of your great-grandfather, please?”

Being asked your birthdate in order to view a game on Steam, and the year dropdown not going back far enough.

I think you’re undervaluing loneliness. Loneliness isn’t just missing some one. Loneliness means there’s no point in connecting with people because they will just die. Loneliness means that no one knows the depth of your condition because it isn’t available to them. It means that as they change and face new obstacles, you’ll be oblivious to all of that. You’ll not only see them die, you’ll see the vitality deep out of their pores as they age. All the while you’ll never know what that means personally or feel that slow slipping.

Also, super weird that your example is a breakup and people dying is something not worth registering.

Repeated surgical corrections for your ever growing earlobes

All the comments assume everybody else isn’t also immortal. I forget the title and author but there’s an old sci fi story (or novel?) about a future where everybody lives for centuries, and they’ve found that the brain only retains a certain amount of experience. They have long careers, get tired of doing whatever, re-educate and do something else, or even have multiple families they eventually forget about. A couple of the characters are surprised to find out they used to be married like a century earlier. To me that seems vaguely like reincarnation, and I kind of don’t hate the idea. I really don’t see any downside to that scenario, or even just going on forever.

People are focused on having regrets and negatives that last forever. But buck up li’l camper, you can learn to move on from stuff. And I say this as a dad whose daughter had cancer at age 10 (she survived). It was hell and I wouldn’t want to live through that whole period again, but I don’t consider it a reason not to want to live forever. The trick is to learn how to cope with these things and not let them outweigh the good experiences you have.

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The rest of humanity will eventually evolve into something you don’t recognize and can never be part of.

Basically all of the time you’re alive will be after the heat death of the universe, where you will be floating in space, with nothing to do, nothing to see, nothing to experience. Complete darkness, complete silence, in a complete vacuum, for eternity. Every other particle in the universe is forever out of your reach. You know that you will have nothing forever. You will never see, hear, or touch anything again, for all of time, which will never end. The trillions of years that preceded your float through the void fade into a distant memory as you outlive twice as much time, four times as much, a trillion-trillion times as much, and infinitely more.

If you have epilepsy or Parkinson’s or MS, you’re just going to likely get worse forever.

People are commenting ‘fates worse than death’ and ‘being made into a labrat by the 1%’, but really, if you have infinite time to just do stuff and you can’t be killed – And you don’t somehow squirrel your way into a position of power then what are you even doing with your time and immortality, oomfie?

The loneliness part is also questionable. I know OP said it’s overly done, but I also think it’s just wrong. If you’re an adult you’ve had people in your life die before. It sucks. You miss them. But then you move on. And you meet other people. You’ll still go “:(” when you think about the person and such… But life goes on.

And that’s just life. It doesn’t get any worse if you extend it longer – If anything it gets better. You might have lost your beloved today, but you have another dozen lifetimes to heal your wounds and meet someone else and fall in love again and (…)

So here’s some lower-stakes, frustrating inconveniences of being immortal:

• Your favourite fashion? It’s not just out of fashion. It’s so out of fashion it is now considered ‘historical costuming’. You can no longer find any articles like it at all. Because the only people even trying to recreate the techniques are costuming nerds and theater people who always exaggerate stuff
• You got a song stuck in your head. It is either from before recording was invented, or any recordings of it that existed are too old to be reliably listenable. You have a song stuck in your head.
• You used to really enjoy a job you did. That entire career path is now obsolete. As per the first paragraph of my post, if you’re immortal you have probably snuck your way into the upper echelons of society at some point during your infinite time… But like. You’re bored. You loved being a Court Jester, now there are no Court Jesters.
• Actually tedium just in general. Sooner or later you’ll run out of new things to try, because you’ll have done everything that even remotely caught your eye already. So what the fuck will you do with your time? You’ll eventually just get depressed and not do anything.

Depends on the type of immorality. Do you continue to age? If no, what age do you stop? Eventually the universe will die. So what happens to you then?

It might be fun for a while. Maybe even a long while. But that fun will be gone in an instant compared to the trillions and trillions of years you will float in a dark dying universe of nothing.

Having potentially thousands of years of embarassing moments of social awkwardness to think about. And, over the aeons, being relieved when the people you know and love die because they won’t remember the things you’re so ashamed of.

If it’s the realistic kind where you just don’t age, the statistical certainty that you’ll eventually die in an accident, or to war or murder. Your odds of getting to the heat death of the universe without making backups is pretty slim.

If it’s the kind where you’re indestructible, you’re highly likely to encounter someone who tries to bury you alive in a subduction zone eventually, because humans are like that, and then you get to spend eternity slowly moving into the scorching mantle.

How much more annoying the (much) younger generations would be.

Losing all of the skills you gain. No matter how good you get at something, after a few centuries you’ll have lost your edge. You can also only practice so many things concurrently without giving something up. At some point, years down the line, you might try to ride a bike again and completely fail to do it, or try to sing and fail to hit all the notes that came easily before, or do gymnastics but the muscles you need are underused. It doesn’t matter that you spent years mastering every skill, your abilities will degrade over time. You’ll never really be able to feel sure about your own abilities except for whatever you’ve done most recently.