'fence-sitter' originates from English, specifically the image of someone who 'sits' on a 'fence' (a physical barrier) implying a position between two sides.

'fence-sitter' grew out of the idiom 'sit on the fence,' which appeared in 19th-century English; the idiom shifted from a literal image to a figurative expression for indecision, and the noun form 'fence-sitter' later developed to label a person who takes that stance.

Initially it referred to the literal act of sitting on a fence; over time it evolved into the figurative meaning of 'a person who avoids choosing sides' or 'an undecided person.'