PRINCIPAL CAUSE

The principal cause of suffering is impermanence, transitoriness, called annica in Buddhism.  Everything in existence is in a state of flux, is changing, ever changing. The Pali word "anicca" literally means "inconstant." 

Impermanence has implications.  We identify with our empirical or egoic self, for instance, saying that this is "me," "mine," "my story."  "I am this one thing."  But since all is transient, there is no such "one thing."  There is no permanent, unchanging, substantial, undeniable self.  The term for this is anatta, no-self.  A socially-conditioned, relative, temporary self exists, but that is all. 

This is frustrating because the person we remember ourselves to be is not the same person who exists in the present moment.  We recall feeling a certain way, happy, sad, angry, etc., in our youth, for instance, but the happy, sad, angry, etc. we feel now is not the same that we experienced back then.  In the same way, we cannot relate to ourselves in the future, how we will feel when we are older.