We can continue to lament the rise of TikTok, and point sagely to the likes of Black Mirror until our pointer fingers fall off. The youths of today have no intention of stopping a very particular way of romanticizing their lives: by pretending it's all one big movie.
It's not groundbreaking to state that it's becoming more common for people, and especially Gen Z, to document their every living moment for the sake of entertainment. When it first became a trend a few years ago, main character syndrome smartly summarized the ways in which the social media native generation conceptualize themselves as the protagonist of their own personal film. It makes it almost surprising that the canon event has taken so long to hit the mainstream.
As the language suggests, the canon event also borrows from basic movie terminology to provide some reasoning for why people do things, or why things happen to them. It defines some kind of occurrence that has a major emotional effect, and shapes the character into who they eventually become (in terms of a filmographic example, some have referenced the death of Uncle Ben prompting Peter Parker to become Spider-Man). In essence, the canon event propels the narrative and potentially creates something great in the wake of tragedy.
One way in which canon events kind of depart from the main character phenomenon is that they are often observed in other people, as well as in ourselves. The phrase is often accompanied by saying 'we/I cannot interfere', underlining this painful yet necessary step. It has even become its own genre of spam comment under controversial TikToks, such as the recent viral video of a woman's boyfriend and best friend play fighting in a way that made many think that she was being cheated on.
All in all, this phrase is fast becoming a handy catchall for justifying our own terrible decisions, and judging those of others. Nothing could be more appropriate for an overly online antihero.