There are a lot of things I blog about that are simply my opinion. I don't consider myself an expert in most things. However, I do have a BA in Psychology and currently work in Youth Services. So, this is one subject I'm excited to write about because I do have some knowledge and experience of it.
5 tips to writing more believable characters based on Psychology.
1. All characters need a backstory: Writing backstory for your character will help your reader understand why they make the choices they make. This may include deciding if your character has a skill that comes easy to them, like an artistic ability that runs in their family [Nature]. It might also include mentioning past experiences that affect how your character sees the world [Nurture]. Psychologists have been arguing for years whether Nature or Nurture affects a person more, but what's clear is that people (and characters) are a product of both their DNA and their environment. Your character's DNA, where they grew up, their family dynamics and things they've been through in their life all affect how your character behaves.
For example, look at Harry Potter. Harry grew into a humble young man who learned to live without under the Dursley's neglect and abuse. Once Harry enters the Wizzarding word he discover's he's basically a celebrity. There are people there who idolize him, and others who hate him, but because of his humble roots Harry remains a character the reader can relate to. Both who he is because of his DNA [the one person capable of defeating Voldemort] and who he became because of his childhood [a humble young man] are important to the story. Had Harry grown up in the Wizzarding world he may have turned into a very different person. Think about where your characters came from, and even if their backstory isn't discussed much in your book, it's important for you to know it as the author. [Keep in mind, however, that Harry Potter was a children's book and much of the Dursley's abuse comes across as comical allowing for Harry to become a humble young man. Had Harry Potter been written for an older audience the things the Dursley's did would have easily been considered child abuse and Harry should have turned out to be a far more traumatized young man.]
2. You must understand your character's wants and needs: Abraham Maslow theorized that people have a heirarchy of needs, suggesting that people need to have their most fundamental needs (like water, food, clothing and shelter) met before they will want to focus on higher level needs. So, how does this relate to writing? Well, your story should be fueled by your character's desires. If you're writing a murder mystery that may mean it's fueled by their want to find a killer. A romance is fueled by your character's want to find love. But, if your character is going to focus on say safety [finding a killer] they need to have their physiological [fundamental] needs met first. If your main character is living on the street they will probably be more concerned about where they're getting their next meal or finding shelter than finding a killer. Not to say they can't do both, but you can't ignore those physiological needs.
For Example, there's a reason why street rat, Aladdin is stealing bread in the beginning of the Disney movie. He's meeting his physiological needs, and later his safety needs with having the genie make him a prince, before seeking love and belonging from Princess Jasmine.
3. What characters think they're supposed to do plays a big role in how they act: Social norms set a huge precedent for how we act. There are things that are expected of people every day. If you have a job, you're expected to show up to work. There are rules of behavior for every area of life. Everything from what we wear, to our greetings, to how we interact with each other is based on a social norm. Do people break social norms? Yes, but not without reason. Your characters should behave in the way that is expected of them in their society, and if they act differently, you need to explain why.
For Example, In Delirium by Lauren Oliver love is considered a disease and it's expected that at a certain age people have surgery to prevent them from feeling love. The main character, Lena, follows these social norms. She takes the tests she supposed to take. She believes the things everyone else believes. Over the course of the novel, she develops different beliefs about love than what society demands, but that only happens after a series of events that change her opinion. The Hunger Games is another example. Katniss accepted that the Hunger Games were a part of life in the beginning of the book, in fact throughout the story her main goal is to return to her life as it was. She accepted the social norms around her. She only became the face of the rebellion through circumstance.
4. Character's shouldn't always say what they mean: People keep secrets, they tell small lies, they keep things to themselves that they'd be better off sharing, and sometimes they just don't want to talk about things that are bothering them. We do this for different reasons. Sometimes, we hold on to things because of social norms. It's not always appropriate to share certain things. Sometimes, we keep things to ourselves because we fear being judged. Your characters should do the same. They may even display Transference, and take out their emotions on people or things that have nothing to do with how they feel. Secrets and inner thoughts can also add necessary tension to your story.
For Example, In Obsidian by Jennifer Armentrout there's a scene where Katy comes up to Daemon at lunch and he's incredibly rude to her. Katy doesn't know this at the time, but Daemon doesn't actually mean the things he says and only does this to try and calm his ex-girlfriend, Ash, who's on the brink of lashing out at Katy. This secret also adds tension to the plot as Katy's feelings are hurt and she then dumps a bowl of spaghetti over Daemon's head.
5. Characters should justify the things they do: Basically, people want how they act to be in agreement with what they believe, and when our action and our beliefs are not in agreement we seek justification to remedy the disagreement. This is called cognitive dissonance. So, how does this relate to your characters? Well, there may be times that your character does something that disagrees with what they believe. Your hero may need to kill someone when they've fought to save lives, or your love interest may try to convince the person they care about most that they can't be together. In these situations it's important to show how your character justifies these decisions or your reader won't believe that they would make those choices.
For Example, In Sweet Evil (and Sweet Temptation) by Wendy Higgins Kaidan believes that he is damned to hell and has a certain life that he has to lead. As a lust Nephilim, he's been seducing women for so long he believes that he needs it and cannot choose to live another way. When Anna enters his life she suggests that he does have a choice. Kaidan finds himself acting differently because of Anna and deals with cognitive dissonance as his actions disagree with his long held beliefs. This comes to a point when he has the opportunity to have sex with Anna -- something he's been trying to do for basically the entire book -- and instead chooses not to. This causes Kaidan distress, resulting in him leaving Anna at the airport instead of continuing their road trip as he feels like removing her from his life will help him find agreement between his beliefs and actions.