Season 1 of Stranger Things started out practical. As the boys searched for Will and learned about the terrors of the Upside Down, they were actively running from a Demogorgon — a flesh and blood monster. In Season 2 and 3, things got a bit more ethereal. There were still monsters like the demodogs and the Spider Monster, but the biggest threat was the Mind Flayer. That made the Upside Down feel more like a shadowy realm, but it also cut down on the tangibility of the threat. So, in Season 4, Stranger Things brought back the flesh and blood monsters by introducing the very-pratical Vecna, who was not only terrifying, but he was also more powerful than Eleven, hence why Dr. Brenner was so afraid of him.

The first reason that Vecna was stronger than Eleven is simple. He was older and more experienced. He was the original subject in Project MKUltra, and using his DNA, Dr. Brenner was able to make or alter the other children so that they would also have powers. Because of that, Vecna was inherently more powerful because he had his powers longer and knew the ins and outs of his abilities.

The first time anyone faced off against Vecna, he was still the murderous Henry Creel. It was 1979, and Eleven had just freed Henry from his Soteria chip, and he quickly unleashed his rage. He always wanted to destroy humanity, so he started with all of Dr. Brenner’s test subjects. Then, Henry tried to get Eleven to join him in conquering the world. Eleven, however, refused and tried to stop him. Eventually, Eleven was able to banish Henry to the Upside Down (where he became Vecna), but it was very clear that Henry had been inherently stronger than Eleven. It was only because Eleven was able to tap into her anger that she was able to defeat Henry.

Having watched the tapes of their first fight, Dr. Brenner knew what Eleven was capable of, but he also knew what Vecna was capable of. Flashforward to 1986, Brenner knew it would be a bad idea for Eleven to fight against Vecna — and he made that abundantly clear. Although keeping Eleven against her will was a problem, he had a valid point, as Vecna “consumes” and takes everything from his victims, including their abilities.

Brenner’s words are the second reason that Vecna was more powerful than Eleven. Vecna had his own strength, combined with the strength of everyone he had killed and absorbed. That means that he wielded his own power, combined with the power of all Brenner’s test subjects and the various monsters he had dominated in the Upside Down.

However, Eleven wouldn’t listen. Like Luke Skywalker in The Empire Strikes Back, she went to fight Vecna before she was ready — and it nearly destroyed her. Without Mike’s encouragement and the whole group’s combined efforts in fighting the Upside Down, Eleven would have fallen and Vecna would have won. After seeing their second fight, it was clear that Vecna was stronger than Eleven one-on-one, so in Season 5, Eleven will have to find a way to upgrade her powers in order to vanquish her foe once and for all.