What is the origin of the idiom "cool one's heels" and when to use it?

The idiom "cool one's heels" originated from the practice of shoeing horses. In the 18th and 19th centuries, blacksmiths would ask riders to "cool" or wait patiently while the newly shod horseshoes were being affixed firmly to the horse's hooves. It is often used in informal conversations or casual settings to describe the act of waiting without becoming impatient or agitated. This expression can be used in a variety of contexts and occasions, such as waiting for appointments, interviews, meetings, or events.