Knowledge-based action, when performed the right way at the right time, has the power to change the flow of any event.
Eren had started studying battle formations ever since he encountered one in real life. He was afraid to admit that Oliver's battle formation had intimidated him.
The butcher had started seeing any lack of knowledge as an obstacle that needed to be overcome. He was like blank paper when he first saw the battle formation's real-time deployment. Combating with a battle formation was like fighting a wild bull with brute strength. Even if he could win the fight, he wouldn't come out of the clash unharmed.
Therefore, Eren decided to dig deeper into this field that he had practically no knowledge of. Being a student of a kingdom-certified academy as well as being influential with money, he had access to various studies done on battle formations and the study of arrays. He started grasping the knowledge hidden in them one step at a time.