What is the origin of the idiom "cry someone a river" and when to use it?

The idiom "cry someone a river" does not have a specific documented origin, it likely emerged organically as a way to describe this behavior pattern in interpersonal relationships.The expression uses the imagery of crying as a means of creating an emotional impact on someone else, much like the imagery of someone crying so much that they could form a river of tears. This expression is used to convey a specific type of emotional manipulation, where tears are employed as a tool to influence the feelings or actions of others.