In the pro-wrestling world, faces and heels are the ideal part of a storyline feud. Faces and heels are what spark conflict between pro-wrestlers. You can have some of the best feuds involving faces and heels but sometimes they don't always work. Why not? Because believable characters are essential to every aspect of pro-wrestling storylines. I will explain what i mean in further detail.
I think many fans can agree that pro-wrestlers such as Stone Cold, Jeff Hardy, Sting, and so forth didn't make it as heels. Why? Because they were pushed as faces to the point where they lost the impact to anger fans as heels. They had no motivation for turning heel. Why would Jeff Hardy work so hard for the fans only to turn on them? He had potential but it was very difficult to make the fans hate him because he had built such a solid loving relationship with them.
It also makes no sense for a face to turn heel or vice versa if there is no motivation, tragedy, or any justification to do so. Believable characters are what matters most. Being consistent with a character's attitudes, beliefs, weaknesses, strengths, actions, words, and so forth is the key to making a successful heel or face turn. It's putting yourself in the position of the character and asking "what would said character do in this situation?" Eddie Guerrero and Mick Foley were some of the few pro-wrestlers who were able to make successful face or heel turns consistent with their characters. Randy Orton was arguably one of the best heels in the WWE because he was consistent with his character from the start. If a pro-wrestler cannot create a balance between good and evil enough to make a successful heel or face turn, he or she shouldn't risk it.
Faces or heels - it makes no difference. What fans should be looking for is believable characters who are able to develop or suffer tragic falls.