A term coined by Hendryk in an older thread discussing the re-imagined Battlestar Galactica series. He was frustrated by the high level of parralelism between the TV show's setting and the present, as evidenced by this quote :
Well, since I've only made it three quarters of the way into Season 2 so far, I'm not reading the rest of the thread which doubtless is awash with spoilers. But I just noticed, in the episode “Download”, that a parking lot on Caprica features a 1960s-era Citroën DS. That rather shoots the suspension of disbelief right out of the air for me. Starbuck's Humvee was difficult enough to accept, but this is a major faux pas as far as I'm concerned. What's next, Admiral Adama driving a Mini Cooper?
He continued his criticism in a later post, postulating the main idea behind the term described on this page :
Well, my question was rather: why an actual song from OTL? Because I feel like filing this under the “Citroën DS incident”, namely a breakdown of suspension of disbelief caused by too specific a reference to OTL.
Though the TV show criticized isn't in the alternate history genre, Hendryk's idea could also be easily applied to AH stories and timelines with implausible or right-out-of-nowhere parallelism - especially ones with a POD far back in history. Too much parallelism - particularly one without any reasonable explanation on part of the writer - could end up being a massive plot hole or at least dealing a heavy blow to the reader's/viewer's willing suspension of disbelief. The Citroen DS Incident could be considered “the lazy approach to world-building” - whether in fantasy, sci-fi, alternate history or any other speculative fiction genre. While writing AH, the best solution is to either avoid it alltogether or try to make it as subtle and plausibly explained as possible.
Far too many parallels with OTL does not an alternate history make ! Parallelism should be used sparsely, creatively and wisely, otherwise it is a very lazy method for writing AH.
Here's a somewhat extreme example, but it gets the message through: Imagine the last ice age never ended. The rough equivalent of European nationalities have a vastly different society, culture and religions than in the history known to us. Who knows, maybe the time is already the early 20th century and these people are still tribal societies and still follow prehistoric shamanism. Now imagine that World War One appears in this ice age version of the early 20th century as well. And it starts for the exact same reasons (imperialism, an assasination attempt) on the exact same date (28th July 1914), with the exact same countries, political alliances, economic (third industrial revolution) and military infrastructure (WWI tech). Well, all this seems quite a stretch, doesn't it? The Europe of this alternate world would logically be very, very different - pretty much almost unrecognizable, and not just because of the different society, culture and religion, but because of a vastly different climate and enviromental situation (for one thing, most of Germany, Britain and northern France would be under the glaciers and everything north of the Mediterranean would be freezing tundra). So, an exact copy of World War One makes utterly zero sense in a Europe still in the grips of an ice age. Being unwilling to understand this and preferring to use “lazy parallelism” instead results in the Citroen DS Incident.
Or, to keep it simple, here's a more tamer example: You have a TL with a widely different history of French automobile manufacturers and companies, yet a Citroen DS exactly the same as (or heavily similar) to the OTL car shows up in production during the 1950s-1970s (and maybe even beyond this timeframe).
The Butterfly Effect - A storytelling convention which tries to find ways on how to avoid the cliché described on this page.