Some day you will die.
Lying on your sick bed about to breathe your last, you will be assailed by every kind of pain.
Your mind will be filled with fears and anxieties and you will not know what to do or where to go.
Only then you will realize you have not practiced well.
The skandhas/aggregates (matter, sensations, conceptions, impulses and consciousness) and the four elements in you will quickly disintegrate, and your consciousness will be pulled wherever your ancient, twisted karma leads it.
Impermanence does not hesitate.
Death will not wait.
You will not be able to extend you life by even a second.
How many thousands times more will you have to pass through the gates of birth and death.
If these words are challenging, even insulting, let them be an encouragement for you to change.
Do not accumulate unnecessary possessions.
Don’t give up.
Still your mind, end wrong perceptions, concentrate and do not run after the objects of your senses.
Be determined not to let your days and months pass by wastefully.
Known as Encouraging Words, this was supposedly written by Zen master Guishan, who lived in the eighth and ninth century A.D. I don't know whether it was really written by him, nor if he really called it Encouraging Words. But I do find it a striking memento mori and call to action.