What this suffix does
-strung forms compound adjectives that describe the degree of tension in a person's nervous or emotional state, using the metaphor of a strung instrument (like a bow or a stringed instrument). High-strung, tightly-strung, overly-strung, loosely-strung — each compound measures the degree of tension in a person's disposition. "High-strung" is the most common: it describes someone whose nervous system seems stretched to a point of easy reactivity, who responds quickly and intensely to stimulation. The metaphor works because instruments strung too tightly snap or produce shrieking notes; those strung too loosely produce no sound.