What is the origin of the idiom "punch above one's weight" and when to use it?

The origin of the idiom "punch above one's weight" is unknown, but it is thought to have originated in the boxing ring. In boxing, a fighter who is shorter or lighter than his opponent is said to be "punching above his weight" if he is able to defeat his opponent. It can also be used to describe a romantic relationship in which one partner is perceived as being more attractive or successful than the other.