4th wall breaking is a reinforcement that the characters are aware of the audience, or are aware that they inhabit a form of media. 4th wall breaking that is specific to comics in interacting with the panel lines, gutters, and word bubbles. The most famous example of this today is the Marvel anti-hero Deadpool, but this has been a style that has been developing since the early days of comics. Examples include: Krazy Kat and Little Nemo’s adventures in Slumberland.
So what why is it so popular that it keeps showing up? Well, part of it is the inclusion of a reader. When addressed directly by a character, the reader feels part of the story, dragging them deeper into the story they’re already enthralled with. It’s an acknowledgment from a person that is enacting the plot you wish to see, like they are showing that the knowledge they are doing this for you. It’s an ego boost. It can also add likability and depth to the characters enacting this behavior. The two comic book characters that are famous for this are Deadpool, an anti-hero psycho assassin; and The Joker, the clown prince of crime in DC’s Batman series. These are characters that canonically that are not questioned when they start talking to no one. The other characters in the comic just take it in stride as part of their personality.
It can also speak to us in an existential way. In “Sammy Sneezes” by Winsor McCay, the panel shatters. Working with the panels can give an unexpected twist to the reader, because they aren’t expecting that aspect of the comic change, because it so rarely does. The characters working with the panel limitations gives the artist something new and fresh to work with, moving outside the limits of panel lines and out to the limits of the page. This has the opposite effect on the reader than the characters directly connecting to the audience. It is most likely to break their suspension of disbelief, but for some reason, audiences often don’t stop reading. It’s accepted by the audience that the comic has identified itself and that it is addressing the constructs that make it so. This recognizing of itself, an imaging of sentience, is not rejected like uncomprehending logic or un-relatable characters. Usually these techniques bring about an existential thoughtfulness to the piece, to break free of bonds of panels or to draw attention to the backgrounds, or to draw attention to the aspects of the comic itself.
Whatever way these characters talk to you, the enjoyment of these connections to the media add another aspect to your media of choice.