My boss ever told me that as a good programmer, who should be able to ensure the code he/she changed must be reliable, correct, thoroughly self-verified, who should completely understand what all the results and impacts that he/she did or revised will cause. I did try my best to be as this kind of programmer, test again and again. But.. bugs are still there. How could I be a zero-bug programmer? know every char of my code will cause and effect?