What is the origin of the idiom "on a need-to-know basis" and when to use it?

The origin of the idiom "on a need-to-know basis" is rooted in military and intelligence contexts. It emerged during the mid-20th century and was initially used to describe the practice of restricting information distribution within these organizations. The principle was that individuals were only provided with information essential to their specific duties or tasks, ensuring that sensitive information was not unnecessarily disclosed. This expression is commonly used to imply that not everyone is entitled to know certain details and that information is provided on a case-by-case basis based on relevance or necessity.