Debord here is saying that human lives become guided by fictions we create, instead of immediate needs. This seems directly connected to the basic idea behind commodity fetishism. We mistake something artificial for something natural. I don't know if he was particularly going for this but ... it makes me think of my own childhood (warning: possible TMI or oversharing), because I was basically raised by the television and had imaginary friends and stuff like that, and didn't know how to interact with actual people. This is maybe a fairly literal interpretation of what he is saying, but it's backed up by what he says later in aphorism 60.
Aphorism 60: "The celebrity, the spectacular representation of a living human being, embodies this banality by embodying the image of a possible role. Being a star means specializing in the seemingly lived; the star is the object of identification with the shallow seeming life that has to compensate for the fragmented productive specializations which are actually lived."
Basically, life as it appears on television/film becomes what people think of as what real life is like and it guides their behavior [and I'm adding this, I don't think he actually says this, but I think it also influences how people interpret other people's behavior. Like how people gauge whether a date went well based on how they see people do it on TV or something]
Dale said during lecture something to the effect of: each chiasmus performs the basic critical gesture of Society of the Spectacle. I was not really sure what he meant by this, but I think I'm figuring it out. The Feuerbach quote in the epigraph to chapter 1 says the present age "prefers the sign to the thing signified, the copy to the original, representation to reality, appearance to essence, . . . truth is considered profane, and only illusion is sacred." Debord is critiquing the contemporary society using this same lens -- everything is backwards. Lies are truth, fiction is reality, appearing is being. This seems connected to the concept of degradation from being to having to seeming. But in that arrangement, there is a middle step. It's not merely reversal from one thing to its opposite. So, then again, if the central complaint in SotS is about this being>having>seeming problem, I'm having a hard time seeing how the reversal of Chiasmus is the same as a one-way, three-step degradation.
Another thought --- I could be a little off on this, because I don't have the text available to me right now, but I remember reading excerpts from Baudrillard's Simulacra and Simulation for another class, and we talked about his concept of the "desert of the real." The real-life example we talked about was Disneyland (I went to community college in Orange County, so this was an easy example), not just the disneyland examples in the text, but the experience most of us had had of visiting disneyland and being exposed to all of its overstimulating, spectacular objects, rides, exhibits, and landscape, and afterward, trudging out to the parking lot -- the "real" world -- and feeling that we had entered into a miserable wasteland of nothingness. The real world we inhabit of littered parking lots, SUVs, exhausted crying children, and smog no longer seems like a world at all, and we're more inclined to ignore it in comparison to the feelings of aliveness that come from being immersed in the colorful, musical, magical world of Disneyland. But both of these worlds are artificial, it's just that one of them is created specifically to help us forget the other. This seemed to be along the same vein of thought, but I'll end my rambling now :)