Between Eren, Armin, and Mikasa, Eren Yeager definitely isn't the brains of the trio. Unlike his two childhood friends, he's no natural-born genius or prodigy. For most of Attack On Titan, he's always been a hothead who punches first and asks questions later. Still, he's grown the most out of the three as the years have gone by, and he's even shown us that he can be a genius when he actually uses his brain for once. He's also full of flaws, leading many of us to question whether or not Grisha made the right choice by choosing him as the inheritor of the Attack Titan. There are references to events in the MANGA, so consider this your one and only SPOILER WARNING.
10 Genius: Infiltrated Marley And Manipulated Falco
We don't blame Eren at all for sneaking away from his comrades during their early days in Marley and taking the situation into his own hands. He managed to keep his emotions in check and disguised himself as an Eldian of Marley without anyone ever suspecting him. Stopping his leg from healing was such a brilliant plan that we would've never thought of! Who could suspect a man with such a grave injury to be a Titan Shifter? He also used Falco to bring Reiner right to him in an enclosed space that gave him the advantage, since Reiner was hesitant to transform due to potentially crushing Falco in the process. On top of that, he used Falco to secretly mail off letters to his Paradis allies, a plan that endangered Falco more than it did Eren himself. After learning that our beloved protagonist was willing to trick an innocent child, we knew that he'd finally mastered the art of war.
9 Not Genius: Thought Grisha's Drawer Was Empty
When Eren tried to use his key to unlock Grisha's basement, we got a little anxious when the key didn't fit. When Levi simply kicked down the door, our first thought was why Eren didn't think of that. Still, we let it slide given that his head was probably still spinning from that backhand Levi gave him earlier. After unlocking Grisha's drawer, Eren was also the first to blurt out that it was empty, but Levi immediately deduced that the bottom was false. Sure, this was an emotional moment for Eren, but he clearly showed us here that thinking outside of the box wasn't his strong suit.
8 Genius: Located The War Hammer Titan's Holder And Found A Way To Absorb Her Powers
At some point during the time skip after Eren and the other Survey Corps members reached the sea, Eren managed to sharpen his observational skills tremendously. During the fight against the War Hammer Titan, he deduced that the Titan was being controlled from a hidden location instead of from within the nape as usual. In no time at all, he was able to pinpoint the location of the Titan Shifter, only to find her encased in an impenetrable crystal barrier.
That's when he came up with the resourceful idea to use the Jaw Titan's powerful teeth to break through the crystal barrier so that he could absorb the power of the War Hammer Titan, putting his own spin on the phrase "make do with what you have".
7 Not Genius: His First ODM Kill
Although Eren's killed a bunch of Titans, we've never really seen him doing so with his ODM gear. In fact, the first and only time he's done so (excluding his takedown of the Colossal Titan) was when he participated in the mission to rescue Historia, Ymir, Connie, Bertholdt, and Reiner from the remains of Utgard Castle. Despite orders for Eren to remain out of the offensive, he decided to go in for a kill anyway. Though he did manage to get a kill in one blow, he had a pretty rough landing immediately after celebrating. Rushing in headfirst like that isn't a sign of a genius, and it definitely isn't a sign of a natural-born leader.
6 Genius: Wrestling In Order To Beat Reiner
During Eren and Reiner's first fight, Eren was completely outmatched. His punches did nothing to Reiner's armored Titan body, while Reiner's punches tore Eren's face apart and sent him flying. Right when everyone thought that Eren would lose, he switched tactics, going for tight holds that managed to crack Reiner's armor. Only a true combat genius could switch his technique so flawlessly in such a drastic situation.
5 Not Genius: Getting Captured By Reiner And Bertholdt
At least in the first few seasons of Attack On Titan, Eren showed us all just how oblivious he could be when his emotions got the better of him. During the Battle of Trost, after one of his teammates had been eaten by an Abnormal, Eren rushed to get revenge, leaving himself open to a surprise attack from a Titan below. It's almost like he gets tunnel vision when he loses control over his emotions. During the climax of his battle with Reiner, he failed to pay attention to the fact that Reiner was moving them not only closer to the Wall, but directly under Bertholdt. Had he been paying more attention, he could've disengaged from Reiner to avoid being kidnapped after Bertholdt's Titan body fell on the two. Instead, he allowed himself to be captured, leading to the death of countless Survey Corps members in that infamous operation to recapture him.
4 Genius: Pretending To Slip Off The Wall To Fool Bertholdt
During the Battle of Shiganshina District, Eren pretended to slip off of the Wall, faking a concussion that caused Bertholdt to focus on Armin instead. While we have to give Armin credit for coming up with this plan as well, it was Eren who not only faked the fall, but landed so that he wouldn't seriously hurt himself in the process, while also positioning himself in front of the hole that Bertholdt created years ago so that he could harden and seal it up while Bertholdt remained distracted. We were shocked ourselves to learn that he had actually performed such a complex maneuver without drawing the suspicion of a Marley-trained scout. Maybe after all this is over, he can just pursue acting as a career.
3 Not Genius: Trying To Push The Colossal Titan Over
Despite being in possession of the Attack Titan and the Founding Titan (two of the strongest Titans out there), Eren has showed us many times that he isn't the sharpest blade in the case. After Bertholdt transformed during the Battle of Shiganshina, nobody could think of a way to bring him down. Eren should've been aware of his strength at that point. He struggled to lift the boulder that he used to seal the hole in Wall Rose just a few months ago, so what made him think that he could actually bring the Colossal Titan down just by pushing on one of its legs? If we're being completely honest, he deserved to be kicked onto the wall after being so stupid.
2 Genius: Tricking Zeke Into Taking Him To The Coordinate
After Zeke and Eren made contact, the two were taken to the Coordinate, where Eren revealed his plan all along. Instead of helping Zeke sterilize all Eldians, Eren planned to use the Coordinate to protect the Eldians of Paradis.
As of Chapter 123, he seems to have accomplished his goal, outsmarting his older brother in a twist that not even Isayama could've seen coming.
1 Not Genius: Trying To Eat Annie Before Almost Being Absorbed By Her
After Mikasa cut Annie's fingers, foiling her escape, Eren nearly consumed her. Though this would've given him an amazing power boost, eating Annie would've been the worst thing he could do. If Eren had actually eaten her, the Survey Corps would've lost out a valuable piece of evidence. Eren nearly gotten himself ensnared in Annie's final hardening, which would've doomed the people of Paradis if Eren spent the remaining seasons frozen along with her. In the words of Levi in the English dub: "It's not a good idea to eat our key evidence, you idiot."