IDIOMS

square peg in a round hole

(idiomatic) Something or someone that does not fit well or at all; something that will not succeed as attempted, except possibly with much force and effort, or alteration of either the peg or the hole or both beyond recognition.

Example: 1919, W. Somerset Maugham, The Moon and Sixpence, chapter 54
  In England and France he was the square peg in the round hole, but here the holes were any sort of shape, and no sort of peg was quite amiss.