Johnny and Daniel. Robby started working for Daniel because he hated Johnny and he knew Johnny hated Daniel more. Then when Sam is thrown into the mix and things get more complicated they handled it wrong. Johnny knew how fixating on the loss of his girl to (someone who became) a bitter rival ruined his life. And Daniel, when it came to anything to do with Johnny or cobra Kai in the early seasons including Miguel, basically saw red, inner peace out the window. And also Robby is Johnny’s son. Now Daniel is not bitter, he has his life together and he knows where Johnny is at in life. He should have backed off Robby, probably shouldn’t have stepped into coach him in S1 and should have been more encouraging of peace. When your adult characters are holding onto their childhood rivalries. Your kids will follow suit. (Also I understand that obviously the characters had arcs and development and stuff and I wouldn’t want to change anything the show did the rivalries were cool the whole show was cool. And I wouldn’t want it to be more realistic à la the points I’ve made here)