Momento Mori is a Latin phrase that was literally coined by early Greek and Roman philosophers. They put thee words on coins to carry with them as daily reminders. Later Christianity incorporated these words into its own teachings as well.
Momento Mori means to remember that you will die. A super positive and joyful thought huh?! Without context it may seem overly grim, but these philosophers used much differently. Remembering this aspect was not depressing, but motivating and healing.
Thinking of your own death relativizes everything else going on around you. It puts your situation in context and trivializes the trivial. When something small is irking you and throwing your whole day off, Momento Mori has the power to snap you out of it. Instead of wasting the precious time you have on this small matter move on and let it go.
This train of thought also teaches you to fully value the moment you are in. It should awaken an appreciation for life itself. Stop and be in the place and time you find yourself instead of always rushing to the next thing. You truly do not know how much time you have so enjoy all of it!
With work or school, games, practices, and training all going on it can be hard to still yourself. Small pet peeves can wreck a whole day if they aren’t acknowledged when you are running around at this pace. In order to be your best at each of the aspects of your life, including sports, you need to practice being here and letting minor frustrations go. The concept of Momento Mori and remembering you only have so much time does just that.