The Peter Principle [1]is the principle that "in a hierarchy every employee tends to rise to their level of incompetence". In other words, workers are tools which are used for as wide a range of tasks as that tool will perform adequately. You can use a Crescent wrench [2]to loosen a nut which doesn’t have rusted threads, but a Crescent wrench won’t transmit as much torque as a 6 point wrench [3] – so when the nut begins to strip, the Crescent wrench has become incompetent to perform the job.
Links:
[1] http://en.wikipedia.org/wiki/Peter_Principle
[2] http://www.google.com/images?q=crescent+wrench&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&source=univ&ei=ynUWTeX7LYmfnAeDn_XwDQ&sa=X&oi=image_result_group&ct=title&resnum=3&ved=0CEcQsAQwAg&biw=1126&bih=660
[3] http://www.google.com/images?q=six+point+wrench&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&source=univ&ei=AnYWTfSIBOXtnQfz94SmDg&sa=X&oi=image_result_group&ct=title&resnum=6&ved=0CFQQsAQwBQ&biw=1126&bih=660
[4] http://www.time.com/time/magazine/article/0,9171,1000155,00.html
[5] http://en.wikipedia.org/wiki/The_Dilbert_Principle