The Mariners impulsive and destructive act in the start of the text is his undoing. The Mariner will discover the consequences of his actions. The simple action of the plot, initiated by the mariner's unthinking, destructive act, leads to his tribulations and consequent process of becoming mature.
The Mariner had shoot an albatross at the start of the story, an act that he deemed casual and without animosity, but actually he committed an impulsive and indestructible act that would cause tons of harsh consequences. He would later come to realize the grave and critical consequences of his casual and harmless act and that he would have to be responsible for it, to be punished for his misdeed and learn for his sufferings that he need to endure during the process of redemption and self-sacrifice.