In the Gay Science, Nietzsche gives us a thought experiment with which to judge whether we are living a good life or not.
He calls it the greatest weight, and its central concept is commonly referred to as the eternal return.
It goes like this.
A demon approaches us one night and says that we'll have to repeat every moment of our life for all of eternity in the same sequential order.
So our existence becomes nothing but a continuous repetition of the same actions and outcomes for all of eternity.
And according to Nietzsche, our response to that realization would determine whether or not we are living a good life.
He wrote: Do you desire this once more and innumerable times more?" would lie upon your actions as the greatest weight.
Or how well disposed would you have to become to yourself and to life, to crave nothing more fervently than this ultimate, eternal confirmation and seal?
So, according to Nietzsche, a good life is one that we would want to live again, a life that we would willingly and gladly repeat for all of eternity without omitting a single thing.
I believe the reason Nietzsche says that a good life passes the test of eternal repetition is because the things that are truly good in life are things that we willingly repeat.
