In order to understand the difference and struggle between Wu Ye and Shi Hai, one must understand how formation works and how talent is distinguished for special occupations like formation or talisman.
Formation is essentially using the environment--like mountain, rivers, location or Feng shui--to borrow or levy the mighty power of Heaven and Earth.
In the early stage of cultivation, formation masters required to use formation flags and origin stone as energy. However, as they grow more powerful, they will slowly abandon exterior aids--even the environment-- and use their cultivation to instantly set up formation.
When it comes to talent, formation masters need to have great calculating abilities to be able to scan and map out the environment. Then, they will need a powerful and sensible soul to be able to engrave the divine runes that make up formations.
