What is the origin of the idiom "spill the beans" and when to use it?

The idiom "spill the beans" originated from ancient Greek voting practices, where a secret ballot involved using differently colored beans. A container held the beans, and when it was time to count the votes, the container would be overturned, revealing the colored beans and thus disclosing the outcome. It is now used to convey the idea of accidentally letting out a secret or breaking silence on a matter that was meant to be kept hidden or unknown.