What is the origin of the idiom "take the plunge" and when to use it?

The phrase is thought to have originated in the 19th century, when it was used to describe diving into water from a high place, symbolizing a bold and decisive action. When applied to marriage, "taking the plunge" refers to the moment when individuals decide to commit to a lifelong partnership and embark on the journey of marriage. This idiom used to describe the act of getting married. It implies a significant and life-changing decision to enter into a marital union. The phrase conveys a sense of bravery, readiness, and willingness to start a lifelong commitment.