The persona is what Carl Jung thought of as the public self. He believed that people are the ones who play a role in a drama and that society is their audience.
When you look at life this way, your writing takes on a totally different slant, regardless of whether you are writing a play, a short story or a novel.
The writer’s job is to write about characters, shaping them with their beliefs. The writer then must create situations whereby the characters reveal themselves to society (the reader) as a result of these beliefs. This is showing, not telling.
A character’s belief system has to be obvious and the actions they take must be consistent with these beliefs. The persona of your character must be maintained throughout the story otherwise your story will be unconvincing and will fall apart. A common weakness that you’ll find in characters portrayed many times today in movies, on TV and in literature is that characters suddenly make an about face in their beliefs. The bad guy unexpectedly becomes the good guy and saves the day; the parent, who has had nothing to do with his kids for years, suddenly shows up on the doorstep and the story ends happily. This usually happens at the end of the story so that the author can tie the whole thing together, and everyone can live happily ever after.
This doesn’t mean that a character can’t change, i.e. conquering his/her fears, or acting for the good of the whole rather than being selfish as they’ve been portrayed throughout the story. But in order to be convincing, you character must have a reason for wanting to make the switch. Their actions must follow a logical path—one that is in keeping with his/her dominant emotions and beliefs. A word of warning: be very careful should you employ a persona switch; it’s been done a million time before.
Remember the old-age question and answer: What do you get when you scratch the surface of someone’s personality? You get more surface!
A persona switch does not happen very often in real life. It’s better to keep your story real. Your readers will appreciate it.