Death.
Eternal life would be great for a few thousand years . . . and then it would just be an endless amount of suck.
Consider Graham's number. Graham's number is one of the biggest numbers used in a serious mathematical proof. It is so big that no mathematical notation can express it, and that if you knew this number, your brain would collapse into a black hole. That is not hyperbole, that is physics. There are more digits in this number than there are planck volumes in the universe, thus the information in your head would be so dense as to collapse into a blackhole.
So Graham's number is calculated in a series of alghorthms. The first of which is:
G1 = 3^^^^3 where ^ us
up arrow notation. Now this number, G1 is an ENORMOUS number as it is.
G2 = 3 (G1 number of up-arrows) 3
G3 = 3 (G2 number of up-arrows) 3
....
G64 = 3 (G63 number of up-arrows) 3
G64 = Graham's number.
Think about this number. And think about this: If you live for eternity, you will live Graham's number years, graham's number of times. And you will live that, graham's number of times again. And you will live
that Graham's number of times. And so on and so forth. You'll live so long that Graham's number of years feels as insignificant as one year, and you'll live infinitely longer than that.
Eternity is long, ridiculously, incomprehensibly long. It is infinitely longer than the largest numbers we can even attempt to imagine.
No. Give me the peace of death when my life has run its course. Living for eternity sounds like a curse.