http://en.wikipedia.org/wiki/Rosenhan_experiment
David Rosenhan – On being sane in insane places – 1973

Reed and weep. Think about it next time u watch one of the many films deeling with this problem, e.g.:
http://www.imdb.com/title/tt0073486/
http://www.imdb.com/title/tt0348836/
http://www.imdb.com/title/tt0172493/
http://www.imdb.com/title/tt1130884/
http://www.imdb.com/title/tt1462220/
http://www.imdb.com/title/tt0824747/
…
http://en.wikipedia.org/wiki/Category:Films_set_in_psychiatric_hospitals