Wake up in the morning and writing down the date of the day with water drops. 

The droplets evaporate slowly, and the date slowly fade away. 

By the time you go to bed,  it will be completely gone. The slow fading of fresh dates allows us to sense through our eyes that a day will gradually, but surely, come to an end.

It does not have to write every day, and it does not matter whenever you do it. Our lives are made up of the accumulation of finite days.

If we can feel such a way on some days, the way how we spend our time will naturally become clearer.