Can coincidence start a plot's trouble but not end it, where does that rule come from, and what do older sources say about where in the outline a coincidence may sit?

The rule appears in two forms in openly readable material. (1) Directional: Mackendrick's 'Slogans for the Screenwriter's Wall' (undated page, (c) Mackendrick Family Trust): 'Use coincidence to get characters into trouble, not out of trouble'; the Pixar list item #19 attributed to Emma Coats appears in a blog post of 11 June 2012 (secondary). (2) Earlier, differently shaped rules: Phillips (1914) names the coincidence that 'helps the author and hero out' (treasure, rescue party) and 'a termination by an act of God' as the failure; Archer (1912) ties acceptability to importance, not direction: coincidences 'become the more improbable in the direct ratio of their importance' and one 'which coincides with a crisis' is 'wholly inacceptable in serious art'. I did not find an earlier openly readable statement of the directional wording; that is a bounded negative (see negative_results). For an outline check the sources support three separate tests: direction (does it hurt or help the protagonist), position (outskirts or the thick of the action), and importance (does the outcome turn on it). Curator qualifications: All 10 excerpts located; the directional rule ('coincidence to get characters into trouble, not out of trouble') comes from Mackendrick's 'Slogans' page, marked (c) Mackendrick Family Trust; short quote only. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://thestickingplace.com/alexander-mackendrick/slogans-for-the-screenwriters-wall/",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://www.goodreads.com/author_blog_posts/2571648-the-rules-of-storytelling-according-to-pixar",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://www.gutenberg.org/cache/epub/70937/pg70937.txt",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://www.gutenberg.org/cache/epub/10865/pg10865.txt",
      "note": "candidate evidence excerpts"
    }
  ]
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