People often report an annoying memory failure when they walk from one end of the house to the other for something and then forget what they wanted when they reach their destination. As soon as they return to the first room, they are reminded of what they wanted in the first place. This common experience best illustrates the principle of

encoding specificity

Explanation:

Based on the scenario being described within the question it can be said that this best illustrates the principle of encoding specificity. This term refers to the principle which states that memories are retrieved with greater ease if the same external conditions are present at the time of retrieval as they were when the memory was stored. Which in this description would be the room.