What is the meaning of the idiomatic expression 'thorn among the roses?

A rose is a plant with sharp thorns on the stems. If you find "a rose among the thorns," you find a soft flower among the sharp thorns. The term can be used to mean anything nice found among not-so-nice things. You might say that someone is "a rose among thorns" if everyone around them is either unpleasant or incompetent.