I can not think of a better metaphor for time passing than this picture to the left.
On our brief getaway to Corpus Christi, My husband painstakingly used the umbrella to draw out our initials and the date and was admiring his handiwork (and I was looking for the best angle to take a picture) as the tide washed it away. He drew it again and we were much faster with the camera this time.
At the time, I laughed and thought it was funny. But upon further reflection, I thought. what would you do right now, if you knew the tide was coming to wash it away.