Thanos’ victory in Avengers: Infinity War is already heartbreaking, but it’s made even more painful by the fact that his success is the direct result of a mistake by Thor — a lone wolf mentality that already proved catastrophic in Avengers: Age of Ultron. Thor’s failure to kill Thanos during the Battle of Wakanda can be traced back to his impulse to act alone. As an Asgardian, Thor typically doesn’t need any help from fellow superheroes to defeat powerful villains. But with Ultron and later with Thanos, Thor’s decision to go solo ends with defeat.
When the Avengers first arrive at Sokovia in Avengers: Age of Ultron they all split off in different directions — Bruce rescues Natasha, the Maximoff twins evacuate the city, and Iron Man, Captain America and Thor battle bots. It’s not a bad initial strategy, but the lack of communication between Thor and the other Avengers comes back to bite everyone involved. Thor’s battle takes him underground, where he discovers Ultron’s plan just in time to watch it come to fruition. If Thor had worked with Iron Man and the others, they may have been able to find the vibranium boosters before they activated, keeping Sokovia on the ground and giving them a leg up over Ultron.
Similarly, Thor arrives late and works alone during the Battle of Wakanda. Thor’s powerful presence initially turns the tide of the fight, but his arrival mid-battle puts him at a disadvantage. Separated from the other Avengers during their confrontation with Thanos, Thor’s attack comes late. Although he is able to successfully use the power of Stormbreaker to mount a strong challenge against Thanos, he can’t prevent Thanos from Snapping out half the life in the universe. If Thor had used the power of Stormbreaker in conjunction with the other Avengers, the battle might have ended differently.
Thor’s overall tendency to work alone comes with advantages and drawbacks. In Avengers: Age of Ultron, he initially leaves the Avengers to seek answers to a hallucination induced by Wanda Maximoff. The knowledge Thor gains in the quest leads to the creation of Vision, who is vital in the fight against Ultron. Thor’s solitude during the early stages of the Battle of Sokovia, however, also leads to a major hit to the Avengers when Ultron manages to get the city off the ground before it is fully evacuated.
Thor repeats this mistake in Avengers: Infinity War when he acts alone against Thanos. Before joining the Avengers on Earth, Thor leaves on a solo mission to Nidavellir in order to get the one weapon he believes he needs to defeat the Titan. Thor does end up with an extremely powerful weapon as the result of the mission — Stormbreaker — but its power alone is not enough. It’s only by working together that the Avengers were able to defeat Thanos. Cooperation was key in their fight against Ultron and it was equally critical in stalling Thanos and pulling off the time heist in Avengers: Endgame.