There is no dispute on the first 2 days
There have been proposals for the 3rd most important day. Rick Warren and Tony Robbins have linked the purpose to fulfillment- when you start living your why.
But for ZYX mindset, the third most important day is the Z- the realization that you, like everyone else, will die. The finite nature of our life, with death and taxes as 2 things that are guaranteed in life, is both a gift and a curse.
It is as bad as an evil witch’s curse on a young baby princess that makes her a sleeping beauty on her eigteenth birthday when she pricks her finger. More than that however, she, her family, and in the fairy tale – the whole kingdom, reacted to the fear of the curse for a much longer time.
Our time in this earth is finite. It has a start and a finish. A third of it we already need to use for sleeping and recharging our mortal body and mind.
So, if we waste time doing things we shouldnt, then we may reach life’s end without really discovering and fulfilling our purpose in this world.
But death, and our awareness of the surety that we will face it one day, is a blessing if we live each day as if it is our last. And our acceptance of this inevitable end, changes our perspective of how we should live our life moving forward.
There are many movies like Brad Pit starrer Meet Joe Black which show how death, and the reality of our death, change how we view the world.
Movies like Charlize Theron Old Guard about the sadness of mortarliy, to the point that death seems a reward rather than a punishment.
So yes, the third most important day in the ZYX paradigm is the day we know we will die, someday which should trigger the X- the things we should not and will not do to achieve our Z in this world.