It seems director James Gunn never quite understood how anyone close to Clark Kent couldn't piece together that he was Superman.
In the comics and most live-action iterations, Clark typically slouches, has a different hairstyle, and pretends to be clumsy and weak in an effort to throw off suspicion.
But Gunn wanted something more substantial for the upcoming DCU feature film, and he found it thanks to the long-forgotten Man of Steel power of Super-Hypnosis.
“That’s canon in the comics,” Gunn told Comicbook in a recent interview.
“It’s kind of been forgotten but that’s from the comics. I was sitting with Tom King, the comic book writer, and I was like, ‘You know the thing that I just don’t really know how to reconcile in myself is the glasses because the glasses always bothered me as a kid.’ They bothered me because I just don’t have that much suspension of disbelief to believe that they're two different people.”
Gunn also noted that while Corenswet’s made pained efforts to make sure that his Clark Kent does actually look different from his Superman, the canonical glasses that hypnotize people to protect Superman’s identity is in keeping with the character's personality.
"Corenswet looks the most different as Clark Kent to Superman, even more so than Chris Reeve. But [Tom King] said, ‘You know, there’s an answer for that in the comics, it’s canon that they're hypno glasses, that they hypnotize people.’”
Super-Hypnosis first appeared in Action Comics #32–33, published in 1940.
The ability later resurfaced in Superman (Vol. 1) #330 in 1978, where it was more clearly explained. In that issue, it’s revealed that Superman uses a power called "Super-Hypnosis" along with his glasses to create the illusion that Clark Kent and Superman are two completely different people.
In that issue, it’s explained that Clark Kent subconsciously uses his Super-Hypnosis to influence how others perceive him. With the help of his glasses, he projects an image of himself as a smaller, weaker, and more unassuming figure. As a result, anyone who isn’t immune to his hypnotic ability sees Clark as completely different from Superman, even if the two share identical physical features.
Gunn goes on to add that he never thought about showing how the hypno glasses work from the audience's perspective, but that he imagines everyone around Clark sees him with a slightly bigger nose and fuller face- essentially sedentary office worker who needs to sign up for some gym classes.