Wikipedia quite rightly wants citations for stated facts and this practice
goes a long way to prevent inaccuracies. But I recall one instance where
it actually caused the establishment of a factual error.
Some city in Germany had a new mayor elected and someone duly updated the
Wikipedia article on the city to reflect this. Another person made a
correction--the new mayor's name had been misspelled. The Wikipedia
editors rejected the correction, citing a published article in a major
newspaper that had the name spelled as it was in the Wikipedia article.
After some back-and-forth the spelling correction was eventually
corrected. It seems that the newspaper in question had gone to Wikipedia
to find out the new mayor's name and so the original Wikipedia misspelling
had gotten published in print.
-Paul W.