What is sehnsucht?

Sehnsucht is a German noun translated as longing, desire, yearning, or craving.

The term describes thoughts and feelings about all facets of life that are unfinished or imperfect, paired with a yearning for ideal alternative experiences.

There is no equivalent in the English language. Portuguese has the similar but not identical term saudade.

For they are not the thing itself; they are only the scent of a flower we have not found, the echo of a tune we have not heard, news from a country we have never yet visited.

C.S. Lewis
The Weight of Glory (1949)