The conjunction rule of probability theory states that a conjunction (A and B) is necessarily less probable than one of the conjuncts alone (A). Any detail you mention explicitly has to be pinned down by a sufficient amount of evidence, all the possibilities and details not asserted can be summed over. Adding more details to a theory may make it sound more plausible to human ears because of the availability heuristic, even as the story becomes normatively less probable, as burdensome details drive the probability of the conjunction down exponentially.