Bingo
"Expect slight inconsistencies and at least one imperfection in a hand-woven rug originating from a country in the Middle East. The philosophy, from an Islamic point of view, is that only God is perfect, and, therefore, nothing man makes should be perfect. A flaw will be carefully woven into each rug." (http://www.homeownernet.com/articles/orientalrugs.html)
No such thing as a perfect terrorist, either...
But there are effective ones.