If you Pigeon Hole a person you're classifying them and giving them a specific identity when more than one might be more appropriate. It used to be common for the English to keep pigeons for food. During the 1900s, offices would have small compartments built into the furniture to file documents and, owing to the fact that they resembled pigeonholes, these also became known as pigeonholes. Each pigeonhole would have a filing category and documents inside would all have a similar theme, decided upon by the filing clerk. Sometimes it was unclear which hole a file should be placed in and so it was up to the clerk to decide where it should go. Hence a document was "pigeonholed" but not necessarily correctly.