Definition & Meaning of "[pour] {one's} [heart] out"

What is the origin of the idiom "pour one's heart out" and when to use it?

The idiom "pour one's heart out" originated from the imagery of pouring liquid out of a container, symbolizing the act of expressing one's deepest emotions, thoughts, or concerns with great intensity and openness. It is used to refer to the act of speaking or sharing in an unrestrained and uninhibited manner, often in a cathartic or emotional way.