Breaking Points
Many characters in Thor allude to how Loki has always been a fan of tricks and mischief. While his antics were sometimes dangerous and led to others getting hurt, I would argue that the degree of destruction is greatly amplified in The Avengers in comparison to Thor. His superiority complex and delusions also are much worse. I honestly think Loki just snapped. He takes a number of blows to his self-esteem and sense of self during the events of the first movie, after all. It seems to me that two specific incidences are "breaking points" for him, in that they augment his already low self-esteem and jealousy of Thor.
1. Odin's confession: The looks on his face and emotion in his voice say it all during this scene. Loki is devastated to learn he is not actually Odin's son, but rather Laufey's. He is the son of someone that terrorized the human race and brought nothing but fear and pain. He is basically the monster that he and his brother dreamed of defeating when they grew up and became king. Loki quickly realizes that Odin took him in for a reason other than out of pity and demands to know what it is. He screams at him to confess, actually. When he perceives he was nothing more than a tool to Odin, Loki's eyes are filled with tears. Odin likely had no intention of Loki ever being on the throne. To Loki, it's no wonder why Thor was always favored over him. Why would anyone from Asgard care about a Frost Giant? Odin tells Loki not to twist his words, but it's too late because he is already beyond reason. The calm and rational Loki becomes completely consumed with emotion. Clearly this event was incredibly stressful for him on multiple levels. The man he admired and wanted to be like was not really his father, his true father abandoned him and left him to die, he sees himself as an unworthy monster, and his dreams of being the King of Asgard are shattered. Who wouldn't be greatly impacted after trying to come to terms with all of that?
2. Odin's rejection: I think Loki honestly believed he would be able to prove himself to Odin by killing Laufey and wiping out the rest of the Frost Giants. I discuss his delusional tendencies on another page, but my point here is that he was overcompensating for the feelings of worthlessness caused by finding out his true heritage. He exclaims to Odin how he could have defeated the Jotuns for him and the good of Asgard as he is dangling off the newly broken bridge to the observatory. His words and face are almost childish in the sense that he desperately wants to please his father. Could Loki have lied and simply used his skillful acting? Maybe. I would argue against that line of thinking though because of what happens after Odin rejects him with a simple, "No, Loki." The light fades from his eyes and face. In that moment, Loki gives up. Letting go of the scepter that was connected to Thor and Odin is likely symbolic of this. He truly believed his actions would prove himself, and yet he was rejected by both Odin and Thor. There was no aspiration left for him in Asgard.
When Loki returns in The Avengers, he is clearly no longer the same person he once was. Not only does he kill a number of people in two days and destroy a large portion of New York City without a second thought, he is also clearly angry. When told he was cast out by The Other, Loki snaps back saying he was a king who was betrayed. Further, when found by Thor, Loki emphasizes that Odin is Thor's father only and becomes visibly agitated when Thor tells him the throne would not suit him. Loki punches him in the chest while walking by and goes on a small rampage about how different he is due to his exile and how he is a king. While Loki is noted as "always" being jealous of Thor by Sif, his jealousy really seemed to be just that—jealousy. He delayed Thor's coronation ceremony with "just a bit of fun," but he never displayed anything more than irritation in the first movie. Such intense anger came about only after he found out his heritage and it was then greatly amplified after feeling betrayed by Odin. Loki no longer had any hope or support to keep him grounded. I am a firm believer in the theory that anger is really a secondary emotion which stems from a more painful one underneath. Anger is easier to deal with than pain. Considering the two "breaking points" discussed above, Loki's feelings of betrayal, disappointment and abandonment could easily fuel the acute fury he displays in The Avengers. Those events shook him up so badly that his anger serves as yet another defense mechanism alongside his delusions and superiority complex.
b a c k . c l e a r . f o r w a r d Loki and Thor are © Marvel and other rightful owners. Sympathy for the Devil is part of AFTER-DEATH.ORG