And the same twofold consideration probably explains the well-known fact that a year seems much shorter to the adult than to the child.

The novel and comparatively exciting impressions of childhood tend to fill out time in retrospect, and also to throw back remote events into a dimly discernible region.
Now, this same circumstance, the degree of vividness or of faintness of the mnemonic image, is that which determines our idea of distance when the character of the intervening experiences produces no appreciable effect.[124] This is most strikingly illustrated in those imperfect kinds of recollection in which we are unable to definitely localize the mnemonic image.

To the consideration of these we will now turn.
B._Indefinite Localization._ Speaking roughly and generally, we may say that the vividness of an image of memory decreases in proportion as the distance of the event increases.

And this is the rule which we unconsciously apply in determining distance in time.

Nevertheless, this rule gives us by no means an infallible criterion of distance.