Here's how it evolved:
* Medieval Logic: In the Middle Ages, philosophers and theologians engaged in intricate debates about minute details of doctrine and logic. They would meticulously analyze arguments, focusing on subtle distinctions and fine points. This practice was known as "hair-splitting" because they were often seen as focusing on extremely minor and insignificant points, like splitting a single hair into even smaller parts.
* The Phrase Emerges: The term "split hairs" was used to describe this overly meticulous and pedantic approach to argumentation. It conveyed the idea of being overly concerned with trivial matters, often leading to pointless and unproductive discussions.
* Modern Usage: Over time, the idiom "split hairs" became a common expression to criticize someone who is overly focused on insignificant details, nitpicking, or engaging in pointless arguments. It implies that the person is being unnecessarily pedantic and missing the bigger picture.
So, "splitting hairs" came to represent the act of focusing on trivialities, missing the main point, and engaging in unnecessary and unproductive debates.