When you have to keep something, such as a promise or a commitment, it is easier to do so when you can remember why you are doing it in the first place.
If want someone to remember, it’s better to tell a story that is universal rather than something specific.
Because not all of us were there when the U.S. invaded Normandy, or when JFK was assassinated, or when the Berlin Wall fell (specific).
However, we can all relate to “I have a dream” (universal).
Universal messages help us relate to one another and cross the boundaries of geography and time. The more universal the message, the faster your ideas spread and the easier they stick – we remember to keep.