“Square peg in a round hole is an idiomatic expression which describes the unusual individualist who could not fit into a niche of his or her society.

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 officer and the office, the doer and the thing done, seldom fit so exactly, that we can say they were almost made for each other.”