Human psychology seems to follow the rule that adding an additional detail can make a story more plausible.

Judged against psychology research as of 2008. The claim is hedged ('seems to'). TRUE: experimental research such as Tversky & Kahneman's conjunction-fallacy studies (the 1983 Linda and Bjorn Borg problems, the 1982 scenario studies) and its replications show that adding specific details to a scenario often increases people's judgements of its probability or plausibility. MOSTLY TRUE: the effect is well documented, but the evidence shows it depends heavily on how the task is framed (e.g. it shrinks with frequency formats), a caveat the hedge only partly covers. MIXED: the evidence as of 2008 is roughly evenly divided on whether added detail raises judged plausibility. MOSTLY FALSE: the effect is shown to be mostly an artefact (e.g. of misunderstanding 'probability' or 'and'), with only narrow support. FALSE: research shows that added details do not increase, or consistently decrease, judged plausibility.

Set before the research began.

1. E1 On the reality of the conjunction fallacy Memory & Cognition (Springer) · 2002

   “Despite the precautions, conjunction fallacies were as frequent under betting instructions as under standard probability instructions.”

2. E2 On Narrow Norms and Vague Heuristics: A Reply to Kahneman and Tversky (1996) Psychological Review (American Psychological Association), via Max Planck Institute PDF · 1996

   “Recent studies using paraphrasing and protocols suggest that participants draw a variety of semantic inferences”

3. E3 The conjunction fallacy? A reply to Bar-Hillel Memory & Cognition (Psychonomic Society) · 1991

   “I do not believe, however, that it is sufficient to account for all of the data.”

E2 (2002) found that conjunction fallacies happened as often under betting instructions as under standard probability instructions. That supports the claim that people judge a more detailed conjunction as more likely, and that this is not just a wording artefact. E3 (1996) shows that before 2008 the interpretation was disputed: critics argued that participants read the problem's wording in different ways. E4 (1991) says one alternative explanation is not enough to account for all of the data. On balance, the evidence supports the hedged claim but shows a live debate about task framing, which fits "mostly true".