At the California Academy of Sciences there is a Foucault pendulum, invented by Leon Foucault in the 19th century to demonstrate the rotation of the earth. It rotates 5 inches every 30 minutes, completing a circle every 30 minutes:
The pendulum oscillates across the center of the circle, and I knew that at some point it would have to move to the side. But staring at it intently I could see no motion and detect no difference between the point that it returned to from one swing to the next.
What other phenomena are similar in that, although we can never notice a change from one instance to the next, we know that there must be change on a broad time scale? Personality strikes me as one example. Although we may update our beliefs on the basis of new facts, our background prior stances remain unchanged in the short run. It is only in the long run that our baseline personalities can change, but these shifts take a long time and are difficult to notice if you remain in daily contact with that person.
Are there personal policy implications to being blind to slow changes in other's personalities?