Relationships are supposed to bring people together. In healthy relationships, boundaries are flexible. We grow and adapt to allow the other person in, but keep the self intact. We give in only so much and will only go so far. We allow the other person into our personal space. We allow them to touch us. We give them access to our deepest thoughts and feelings. If someone uses that access to harm us, it is betrayal of the highest order.
Most of your characters would be hard-pressed to vocalize what their boundaries are, but feel violations all the way to their core. Boundary violations can inspire heated arguments, divorces, revenge plots, and serve as motive for murder.
1. A woman who tries to get too close too fast will unsettle Dick. He will either decide that she is up to something or that she is emotionally unstable. If he is at first flattered by the attention, he will soon realize that he should have been more wary. Such is the stuff of many a horror story. Romances thrive on love at first sight and sex with a stranger, but that is rushing intimacy. In real life this scenario typically does not end well. That level of intimacy implies connections that haven't been formed yet. It is forcing a character to trust someone they don't know with their health and welfare. It is a boundary violation that runs rampant throughout modern fiction. It's also a plot hole, especially when it happens because "the script calls for it."
2. A character who offers too much personal information too soon will make Dick suspicious. This is effective as a plot complication. However, if a character enters the story and shares way too much personal information for no reason apart from delivering information, it becomes a plot hole. Readers will be irritated by it, unless they relate to the situation because their own boundaries are fuzzy.
3. Readers sense boundary violations in your story. They won't necessarily stop reading to shout, "Their boundaries are off!" Rather, they stop reading because they don't like the characters or think the plants and payoffs aren't realistic. I have tossed several books aside because the protagonist fell on either extreme end of the unhealthy boundary spectrum. This is often true in Thrillers where the protagonist runs around shooting people in a display of badass. Protagonists without conscience don't feel particularly heroic to the reader. They may still root for him to succeed but they don't necessarily like him. It may turn readers off so that they don't read the next book in the series. We want our heroes to care. They may have to take drastic measures to save us, but we don't want them to be the monster, even if you are writing paranormal.
4. Con men often approach and get real chummy too fast. Dick takes the stranger at face value initially. Unless Dick is professionally trained to detect liars, he won't stop to think, "this man is being way too friendly." Instead his intuition will tell him that something doesn't quite add up. As you relate Dick's responses, your reader will feel that same tug of intuition. As the plot progresses, Dick will begin connecting the dots and the reader will too.
5. At the extreme end, characters lacking sufficient boundaries remain in toxic, even abusive situations, befriend serial killers, or allow other characters to walk all over them. Most characters fall somewhere in the middle or slightly off center on the fuzzy-rigid spectrum. Circumstances can force any of them to be slightly rigid or slightly fuzzy.
6. On the mild end, they enable their children, can’t say no to excessive overtime, think celebrities are actually friends, or insist on taking photos of their butts on the company copier during the Christmas party. They cling and make outrageous demands, manipulate through guilt, or spend their time trying to fix broken people. They expect to be admired for their sacrifices and outrageous efforts to please and repair.
7. Use characters with poor boundaries to complicate Dick's life. If Dick is the responsible hero type he will try to drag this person back to a healthy sense of self or convince them of the error of their ways. In the end, unless it's a biography or a down-ending tale, Dick should be willing and able to accept that he can’t and isn’t responsible for fixing them. Even if it means losing them or letting them self-destruct. He may get sidetracked or dragged down temporarily by the toxic character, but his boundaries should be healthy enough for him to know when to walk away.
The toxic character may make solving the overall story problem next to impossible. Your antagonist, if you have one, is often toxic or is surrounded by toxic types enabling his erroneous ways.
8. A fairly well-balanced Dick can be driven to some derivative of fuzzy or rigid behavior depending on the circumstances. He would have to tolerate incursions to work for a rigid character. He would have to become a bit rigid when solving a problem with a fuzzy character. Extreme circumstances can force him into extreme behaviors.
9. If Sally has a weak sense of self, she’ll find it difficult to distinguish herself from the characters she forms relationships with. She will use the other people to fill in her missing pieces or the emptiness she feels when she is alone. The problem is, no one can do that for her and no amount of trying will make it so. It could show growth if she starts off a little insecure and grows into confidence. However, characters with a truly weak sense of self make poor protagonists. I could list a few contemporary examples.
10. If Jane is rigid, she will find it difficult to adjust her boundaries to allow the other person in. She ends up in emotionally detached relationships and is incapable of intimacy. She will make a lousy friend and a difficult lover. Rigid characters make excellent antagonists and foes.
11. Put fuzzy Sally with rigid Jane and you have a neurotic, passive-aggressive relationship. Their opposing approaches will make anything they undertake unsuccessful. They will get frustrated with each other and constantly return to the arena to repeat their tug of war.
Pair a healthy Dick with a rigid Jane or fuzzy Sally and the game is on. They will disagree verbally, thematically, even physically.
12. Dick can fear hurting someone he cares about, so he gets a little fuzzy. It’s easy to kick out a terrible tenant. It’s harder to evict an aging father with a Vicodin habit.
If Dick has healthy boundaries in all other respects, he may get fuzzy when it comes to dealing with a wife who is emotionally abusive due to mental illness or a child who has violent outbreaks.
Boundary conflicts can be a thematic argument, an overall story problem, a disruptive factor at scene level or serve as a motive. It can complicate things for your protagonist in any story.