To me, mastering needlework is like being a great cook. In both cooking and stitching, one starts off a little timid, always making sure that the recipe won't be "above your level", wanting to stick exactly to ingredients on the menu (Aida=Jiffy mix?). As you progress, you become more comfortable, able to make substitutions, making the recipe or piece your own. You also become knowledgeable about what works in certain situations; which threads work with a certain technique in the same way that a spice works best with a particular dish.

So I think a master stitcher, like a master cook, has a broad knowledge of techniques and skills, and perhaps the history behind them. Instead of relying on the aesthetic of others, they have their own sense of beauty and how to create it. I think a master stitcher also fosters the creativity of others - I've always felt inspired after looking at the work of a really good stitcher.