Board Thread:Rebirth: Applications/@comment-26116209-20141103024958/@comment-1875854-20141105214712

Okay to be sure then, why did Darui teach his old friend Black Lightning? Darui is loyal to the village, and seems like to be Shai's mentor if anything.

What this means is, there hasn't been a real compelling reason to why Darui would teach him. Could Shai have lied to him about why he defected? Sure, but then that doesn't explain why Darui would teach him. At the end of the day, he still defected. If you want to say he cast genjutsu to make him teach him, that's different. But unless Shai genjutsued him to make him believe that he was going to return to the village, it doesn't really come together why he would teach him. Old friends, sure. But he still left.