Suppose that you are in the top floor of a library, and you suddenly think about some information you need on the main floor. You return to the main floor and find that you can't recall what you needed. After returning to the top floor, you recall instantly.

you forget what you had in your mind

Explanation:

you cant remember what you were thinking.

This is an example of The encoding specificity principle.

Explanation: This principle was introduced by Thompson and Tulving who suggested that contextual information is encoded with memories which effects the retrieval of said memories. This principles illustrates that matching the encoding contexts of information at recall assists in the retrieval of episodic memories.