Leben means "life" and a Künstler is an artist. Lebenskünstler refers not so much to people who turn their life into a piece of art than to people able to face whatever life throws at them with equanimity and a minimum of fuss. It's not so much that they see something positive in every situation (a form of self-delusion); rather, they always seem to find a way out of problems they encounter without kvetching and self-dramatization. It's also not a matter of "grace under pressure"Lebenskünstler don't let pressure get to them in the first place.
As you may guess, I have great admiration für Lebenskünstler and wish I myself had more of one in me. I'm surprised that there does not seem to exist an English equivalent with exactly the same shade of meaning.
Note: Attentive readers will have noticed that I have been using Lebenskünstler also as a plural. This is correct: It's one of the German -er nouns whose plural is the same as the singular.
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