People talk about spend and replace.
What if there is nothing left to replace the spent #bitcoin?
What if there is no fiat left to spend?
Congratulations, you understood what money is.
Discussion
Unfortunately people have a lot of theoretical knowledge today but zero practical knowledge. Most hope they could live just with investments but the sad reality is that Bitcoin or not Bitcoin in a not so distant future by AI and robots most people will have nothing to exchange because time itself is a value only for ourself.