The phrase originates from nautical terminology. In sailing, "by" and "large" have specific meanings related to the wind and the ship's direction.

• By: This term refers to the ship sailing "by" the wind, meaning as close to the wind as possible. A ship sailing "by the wind" is sailing almost directly into the wind, which requires careful navigation. 

• Large: This term refers to a ship sailing with the wind coming from behind, or "large," which means the wind is blowing from a favorable direction, allowing the ship to sail with ease. When sailors used the term "by and large," they were referring to a ship's ability to sail both "by" the wind (close-hauled) and "large" (with the wind from behind). Essentially, it indicated that the ship was versatile and could handle various wind conditions. 

Over time, "by and large" transitioned from a specific nautical term to a more general idiomatic expression in English. It came to mean "in general" or "for the most part," reflecting the idea of being able to handle different conditions or situations effectively.