sunhou writes: "The AMS published a lecture by Donald Knuth called All Questions Answered (pdf), where Knuth simply responded to questions from the audience. Topics ranged from errors in software ('I think Microsoft should say, "You'll get a check from Bill Gates every time you find an error"') to how he gets distracted by fonts on restaurant menus, to software patents. There were some really good questions (and responses)."
Computers are unreliable, but humans are even more unreliable.
Any system which depends on human reliability is unreliable.