When we have unfinished tasks, we think about them continuously. But the moment they are completed, we forget about them. If we have unread email, we constantly wonder what it says. But once it has been dealt with, we often cannot recall the details of it.

Once our brain receives information, it temporarily stores sensory memory (sight, hearing, smells, taste, and touch). If we pay attention to the information, it moves to our short-term memories.