transience

/ˈtrænziəns/

If your grandmother is always talking about how quickly the years go by, she is focused on life's transience, or briefness.

Summer's quality of seeming to be over just as it's started can be described as transience — anything that feels impossibly brief has that same attribute. People most often use the noun transience when they're talking about good things, like beautiful days, a nice life, or a fun vacation, that seem to be over in an instant. The word comes from the Latin transiens, "passing over or away."

Definitions of transience

1. noun

   the attribute of being brief or fleeting
   synonyms: brevity, briefness

   type of:

   duration, length

   continuance in time
2. noun

   an impermanence that suggests the inevitability of ending or dying
   synonyms: transiency, transitoriness

   types:

   fugaciousness, fugacity

   the lack of enduring qualities (used chiefly of plant parts)

   ephemerality, ephemeralness, fleetingness

   the property of lasting for a very short time

   type of:

   impermanence, impermanency

   the property of not existing for indefinitely long durations