So my body is immortal (Biologically, does not age).
I even moved my brain into a floating rejuvenation tank with a huge cyborg body. But now what?
A thousand years will pass and normal people will still die, get born and mutate. I on the other hand is stagnant.
After another thousand years, humans have become so smart and improved that I have become what the apes are to us today.
There goes my dream of immortality down the toilet. Even if it was possible. Cheating nature would completely stop my own development while new humans benefit from thousands of years of evolutionary improvements. To the point where in their eyes, I am nothing more than a mechanized monkey to be made fun of.