The web resource of the quote: Carl Jung Depth Psychology Blog
From C. G. Jung’s letter to J. Allen Gilbert. At the time of his last letter G. was 78. He died at 81.
At your age I shouldn’t worry any more what one could do with your life.
You should rather think of what you still can do with it. And in your place I wouldn’t seek such an experiment as it is already near at hand, because the end of life will put you exactly into what you always tried to get into.
But unfortunately you tried it in an indirect way and under the guidance of somebody else.
But when you die, nobody else will die for you or instead of you. It will be entirely and exclusively your own affair. That has been expected of you through your whole life, that you live it as if you were dying.