Larry Sanger in the paper “The Fate of Expertise after Wikipedia”:

Over the long term, the quality of a given Wikipedia article will do a random walk around the highest level of quality permitted by the most persistent and aggressive people who follow an article.

Larry Sanger is co-founder of Wikipedia but left years ago. You can read the hyper-interesting account of his involvement with Wikipedia in “The Early History of Nupedia and Wikipedia: A Memoir” (part 1, part 2).