Wikipedia:Source your plot summaries

Wikipedia articles concerning fiction frequently feature overly long or excessively detailed plot summaries. While any plot section can be trimmed, it can be hard to know what to cut if one hasn't consumed the relevant media, while those who have might be tempted to explain any intricacy that arises to give the reader the full experience of the show. This essay offers a solution: sourced plot summaries.

Reasons to source plot summaries
On Wikipedia, editors are not required to use secondary sources for plot summaries per MOS:PLOTSOURCE; the reasoning goes that it is generally assumed that the work itself is the primary source for the plot summary. However, relying on this can lead to original research and overly long summaries. Sourcing plot summaries provides clear benefits in terms of overall encyclopedic value to the reader.

Verifiability
Articles on fictional works often cover something a future article editor would never read; novels in genres they have no interest in, TV shows on streaming platforms or channels they don't have, movies in languages they can't speak or translate. Given this, while any editor can in theory verify a plot summary by gaining a detailed understanding of a work in order to find out what's important to the plot, this isn't a widely-utilized solution in practice. Basing plot summaries on reliable sourcing allows the next reader to reassess and re-evaluate the length and content of the plot summary with the same agreed-upon and widely accessible yardstick, thus minimizing the risk of original research slipping in.

Minimalism
It seems not unreasonable to speculate that articles about fictional works have a tendency to be written by fans of the work, and that the in-depth knowledge of a work's plot possessed by a fan tends to lead to plot summaries stretching for too long, giving too much detail. Pieces of trivia and other cruft can frequently work their way in, and without having read or watched the original, it can be difficult to know whether the relevant piece of cruft is actually important. By referencing sources for a plot summary, editors can check whether a given fact discussed in enough detail to be relevant, or if it's even mentioned at all. Relying on organizations that have more rigorous editorial processes helps keep the information presented by Wikipedia minimal, relevant, and encyclopedic.

Fictional characters
Articles on fictional characters arguably suffer from long and irrelevant plot summaries more than their parent works. Characters can build up long, complicated backstories over years in their movie franchise or book series or television serial; and in an absence of abundant coverage, editors may be tempted to revert to writing long "character biography" sections as a substitute for real-world encyclopedic content. There is a better way; character articles are prime targets for mixing real-world, reliably sourced interpretation with canon. Instead of giving a complete history of the character's appearances and little details found in flashbacks, consider using reliable sourcing to talk about the character's personality, their strengths and weaknesses, how and if they evolve, and if there are weak points in the character's writing or portrayal. Utilizing reliable sourcing in a character's article can provide a clearer, broader set of topics that appeal to all readers, and not just fans.

For non-fiction, too!
This problem isn't limited to works of fiction, either; political books, documentaries, scholarly articles, and history books all have lots of content that might need to be summarized if the work qualifies for a Wikipedia article. However, for political books especially, the main idea should not be to summarize every point and argument made, or even the ones that stand out. By referencing reliable sources, critical review especially, editors can get an idea of what parts of the argument are most important, and allows for a minimalist argument summary that is still a valid and comprehensive reference for the reception section.