What is the origin of the idiom "the last straw" and when to use it?

The idiom "the last straw" is used to describe a situation or event that becomes the final and decisive factor leading to a particular outcome, often a negative or breaking point. It originates from the proverbial expression "the straw that broke the camel's back," which refers to the idea that a camel can carry a heavy load, but adding one more straw will cause it to collapse.