against the grain In opposition to one’s basic temperament, against one’s will. In this expression grain refers to the direction of the fibers in wood. Planing across the natural direction of the fibers is difficult. By analogy, the grain has come to mean the human disposition or will, as exemplified in the following:

A second explanation is that the phrase came from the French contre le gré ‘against the will,’ partially translated into English as against the gré, and so used by Samuel Pepys in his Diary.

fish out of water A person not in his regular environment; one working in a job unrelated to his chosen profession; someone who is restless, fidgety, or discontented because of his surroundings. A fish taken out of water begins flopping about in a desperate attempt to return to its natural habitat. Eventually, the lack of its regular environment kills the fish. Thus, a person who is restless or uncomfortable because of strange surroundings is often likened to a fish out of water.

a square peg in a round hole A person whose job is completely unsuited for him; a person who attempts a project or undertaking which is incompatible with his skills and background; also, a round peg in a square hole. This self-explanatory expression retains frequent use today.