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The twin tropes you are referring to are Deus ex Machina and Diabolus es Machina. In both cases an event comes out of nowhere, not foreshadowed, to effect a drastic change. Both tropes are frowned...
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#4: Attribution notice removed
Source: https://writers.stackexchange.com/a/47395 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/47395 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
The twin tropes you are referring to are [Deus ex Machina](https://tvtropes.org/pmwiki/pmwiki.php/Main/DeusExMachina) and [Diabolus es Machina](https://tvtropes.org/pmwiki/pmwiki.php/Main/DiabolusExMachina). In both cases an event comes out of nowhere, not foreshadowed, to effect a drastic change. Both tropes are frowned upon. For example, Marion Dane Bauer in her book on writing, would say to her writing students "If you end your story by having your main character get hit by a truck, you have just flunked." (taken from the above tvtropes link, didn't find original source) There is _a little_ more leeway with inconvenience than with convenience: an additional challenge for the characters to face is more interesting than the challenge getting solved all by itself. Nonetheless, "things going wrong" would usually take the shape of "everything that could go wrong, goes wrong" - things that are plausible within the story. (On the flip side, if everything goes according to the best-case scenario, it's a bit underwhelming.) A problem that comes out of left field, particularly in the last part of the novel - it's not a good thing.