What is the origin of the idiom "iron in the fire" and when to use it?

The phrase "iron in the fire" originated in the 16th century and referred to the practice of blacksmiths heating multiple pieces of iron in a forge at the same time. The term "iron" is used metaphorically to represent a project or plan, and the "fire" symbolizes the energy and effort devoted to it. It is used to describe a situation where someone is working on multiple projects or plans simultaneously.