Why John Cena turned Heel?

I discuss the HUGE unexpected John Cena Heel Turn at WWE Elimination Chamber, how this will effect the Road to Wrestlemania 41 and the story arc to the end of John Cena's wrestling career. I discuss the Pros and the Cons of the Heel turn and answer the ultimate question: Was the heel turn at this extremely late stage of John Cena's professional wrestling career a good decision?