The geometry of your trade.  For software developers, it seems one gets a robust feeling for this geometry (he or she masters the craft) after about a quarter-million lines of code. Many of those who mastered the craft grew beards and wear leather jackets. The rest probably became managers.  -- PhilipEskelin

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Accompanying the quarter-millions lines of code are thoughts like "Hmmm, this could be better, simpler, clearer for the next programmer, easier to enhance and maintain."  These thoughts are followed by action, which flows naturally from reflection on a problem, and knowledge imparted by authors -- a very select few -- who themselves are masters of TheCraft. --JoshuaKerievsky

Who would you consider as being MastersOfTheCraft.
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See PointAndClickDragAndDrop for one answer to which this page is pointing.