Here's the breakdown:
* "Overboard" literally means to fall or be thrown into the sea from a ship. This was a serious danger for sailors, as it could lead to drowning or being lost at sea.
* "To go overboard" in the literal sense meant to physically go over the side of a ship. However, it was often used metaphorically to describe someone who was excessively enthusiastic or zealous about something, perhaps to the point of being reckless or foolish.
* The metaphorical use of "to go overboard" eventually evolved into its modern meaning: to do something to an excessive degree. This could apply to anything from decorating a Christmas tree to expressing your love for someone.
Examples:
* "He went overboard with the decorations for his birthday party."
* "She went overboard trying to please her boss."
* "Don't go overboard with the food, we're only having a few friends over."
So, while the phrase originally referred to a physical act of going over the side of a ship, it has since become a widely used idiom for overdoing something, often with humorous connotations.