Memento Mori is remembering that one day you will die.
You can choose to face this fact with fear and dread, or you can use this knowledge to experience every moment that you have as a gift. The choice is yours. Over centuries, and in many cultures and philosophies; from the Stoics of Ancient Greece and Rome to the Japanese Samurai, this wisdom has enabled people to focus on what is truly important to them. Acknowledging that you are mortal can allow you to experience a true sense of freedom and purpose.
This is not a discovery. It’s a rediscovery.
Memento mori on Wikipedia
The Obstacle is the Way: The Ancient Art of Turning Adversity to Advantage Paperback – 4 Jun 2015
by Ryan Holiday – a good overview of stoicism.