Highly strung

Hi, I am trying to find the origins of the saying 'highly strung' as in: "He/She is highly strung" meaning "he/she is a bit tense'.

Why highly strung though - where did it come from?

RRC provided an origin from musical instruments. The phrase (usually written "high-strung") may come from archery. Besides its meaning of nervous tension, "high-strung" has another sense: it's a synonym for "overstrung," said of a bow whose string is too short. I don't know which is the real origin; both are lausible. ~rb