At the beginning of “The Eight Mountains,” the stunningly beautiful and deeply affecting adaptation of the award-winning novel by Paolo Cognetti, our narrator, Pietro (Luca Marinelli) describes a unique kind of friendship, one that has offered him “a place to put down roots.” Roots and rootlessness are at the core of this simple, yet complex tale, one that drives at the very heart of existence, our connection to others and to the world around us. This French/Italian/Belgian co-production is written and directed by the Belgian husband and wife filmmaking team of Felix van Groeningen (“Broken Circle Breakdown,” “Beautiful Boy”) and Charlotte Vandermeersch, who delicately balance the earthiness, effervescence and emotional highs and lows of this story.