Balancing Rocks

Along with the serious side of dry stone work,many wallers enjoy the challenge of sitting rocks one on another.While this is good fun it seems that some of us have much more success than others.I wonder what exactly is required for this skill .Is it careful choice of the stones,artistic ability ,a steady hand or some innate characteristic?Whatever it is I wish I could do it better.

This photo was sent by Evan Oxland.