I was spurred to repost this by the discussion of testing and the idea that even programmers who test their code can submit flawed algorithms. The epigram "Programmers are not to be measured by their ingenuity and their logic but by the completeness of their case analysis" came to mind, and here are all of Alan Perlis' brilliant observations for another look.
This is one of those classics that deserves to be reposted every few months. Upvoted.