"Square peg in a round hole" is an idiomatic expression which describes the unusual individualist who could not fit into a niche of their society.
[1] The metaphor was originated by Sydney Smith in "On the Conduct of the Understanding", one of a series of lectures on moral philosophy that he delivered at the Royal Institution in 1804–06: If you choose to represent the various parts in life by holes upon a table, of different shapes,—some circular, some triangular, some square, some oblong,—and the person acting these parts by bits of wood of similar shapes, we shall generally find that the triangular person has got into the square hole, the oblong into the triangular, and a square person has squeezed himself into the round hole.
The British novelist Edward Bulwer-Lytton published the metaphor in a late 19th-century book: Kenelm Chillingly asks, "Does it not prove that no man, however wise, is a good judge of his own case?
It is used in a range of contemporary business-related circumstances; and illustrative examples include: The idiomatic expression conjures a visual image, and this is evolving independently, e.g., Sejong the Great of Korea commented, in 1443, that using Chinese characters for Korean was “like trying to fit a square handle into a round hole”.
There is a Chinese idiom "方枘圆凿", or "方凿圆枘", (literally and respectively "square tenon and round mortise" and "square mortise and round tenon") that was originally derived from a line in the Verses of Chu (Chu ci) 楚辭), composed in the Warring States period (ended 221 BC), in which the poet Song Yu writes: "圆凿而方枘兮，吾固知其龃龉而难入。" The Han Dynasty historian Sima Qian and Tang Dynasty historian 司馬貞 used the same expression in their historical writings too.