What is the origin of the idiom "right as rain" and when to use it?

The idiom "right as rain" is thought to have originated in the 19th century and is used to describe something that is in perfect condition or working order. It likely draws on the idea of rain being a natural element that brings freshness and nourishment to the earth. It is used to convey that everything is well, satisfactory, or resolved. This idiom is commonly used in everyday conversation and writing to express a sense of correctness or completeness.