How to write about a character adversely different to you

• You could think "How would I respond in this scenario?" and then do the exact opposite.

• You could give your mean character a behavioral pattern that is simple to you but deeply engrained and maybe complex to them. All their knee-jerk reactions follow this track (maybe they always defend themselves, or always roll their eyes, as a result of their pattern of closing themselves off and deflecting. Or they overreact and attack the person who makes them angry they have a pattern of going on the offense; they're a fighter.). This ties to AmaiKotori's thoughts a little bit - I like her answer.

• If I'm understanding your question correctly, you are stuck on how to make your fundamentally hateful character want to help, which goes against her default state. If that's the case, maybe you need to make sure her reason for wanting to help is super important and she must do it. Maybe the reason actually deeply stems from self-interest. Maybe she has a pause moment where she basically thinks, "This isn't like me. What the hell?"

• If you have her around other characters who, say, are more like you (kind-hearted), you could make their differences in values/behaviors very apparent. If another character says something about your mean character's attitude, it can drive it home with the reader.

• Good point on touching on backstory, too. I've heard that if you have a backstory for your character that you understand, and it ties into their strengths and weaknesses, they should come off as believable.

Have fun with it. How humans work is fascinating, frustrating, and awesome to dive into. Hope this helped a little bit. Just some random ideas I've learned and heard. Remember that characters are just people - but imaginary. People change. Don't forget that they can rectify their ways (like for my first point, the engrained pattern can be upended). Because all good characters change, right?

For me the primary way to write any character (or to write parts of a character) that are different than myself is to study that archetype in films and in person and in books, sometimes letters even.

I also give my characters personality types according to multiple personality type tests (I find Enneagram the most useful but also use Myers Briggs and Life Languages).

Finally, for those that I am really struggling with, I compile not just a backstory, but another document that lists all their traits from different personality tests as well as brainstormed phrases they say and other conjectures I have reached. When I'm getting ready to write one of their scenes, I read over that document first, each time.

The question boils down to the following: "How do I learn to use language efficiently, be imaginative, and become a successful writer?". Forgive me for saying this, but this is way too vague. There is a reason why writers need real life experience before they proceed to write. I find it hard to write mean characters for the same reason: I am a good person. But I have seen so much evil, that now I know how to describe it. 20 years ago I could not.

Some say the best way to write about characters is to study their faces when situations are presented to them. A good example of this is Dubliners by James Joyce, for he makes excellent observations on faces. Basic facial responses to situations may disclose much about a person.

In short, the way those that draw make studies of portraits with sketches may be analogous to a writer’s approach.

The next step is to bring that into both dialogue and intention, but this part requires depth both philosophically and psychologically, as one must ask why a character behaves this way or that. A more important question is asking what a character believes, and this is a gem brought down in Platonic dialogues. Characters in those dialogues are always pressed for beliefs, and one wonders why Plato did this, but this is better unraveled through examination in practice for your characters.

Plato is insightful with badgering for belief and Joyce for examining the face, and it would help to study them.

Not much depends on making oneself relative to this person or that in writing characters, for maybe then characters are limited by a focal point of beliefs, but on assessing beliefs and actions as a result of such beliefs. Do certain beliefs lead one this way or that? If not now, then will a belief lead this way or that? And this is where the philosophical element comes in, not one where one knows what Platonism or Aristotelianism is, but where the writer is hard pressed to explore another person with fundamental questions on love, life, death, and the metaphysical—this requires but curiosity and heart, not formal education, however, it doesn’t hurt to have such education.

This is similar to working with coworkers you do not get along with where, if you knew them, although both ultimately disagree on a fundamental value, you are pressed to ask if you would still have compassion for them: are you capable of such introspection? (The writer is not saying that you are not, but states the question out of necessity)

Such is the case for a writer, it seems.

Close your eyes, leave the keyboard alone for a bit, and imagine yourself as the character—but not at the point you're having trouble writing. If this is the first time you've immersed yourself in their head, start from the beginning. It sounds like you've got a good idea of the events that made them the way they are, so work your way through those events, imagining them as vividly as you can. Make sure to use the first person in your thoughts—I did this, that happened to me—and keep your metaphorical 'viewpoint' firmly behind the eyes of the character, not as an outside observer. This part should give you a good base for sympathizing with the character.

Now, while that's a start, there's also the way the character handles their emotional reaction to events. Everyone experiences negative emotional reactions, of course, but while it sounds like you're probably used to handling those quickly and moving past them, it's not uncommon for people to dwell on their anger, hurt, frustration, etc. until a different reaction to the event, person or situation in question is very difficult.

Think back to a time when you had a similar negative reaction to something, one that was more difficult than usual to move past. Spend some time thinking about things you could have done differently to 'win,' who was most at fault for various aspects of the situation, shifting blame away from yourself when you can get away with it just for practice. Once you're used to the feeling, return to the character's perspective and apply that spiral of negative emotions to the events in their background: everyone really is set against them, and each successive negative outcome is only demonstrating the point further. Positive outcomes are flukes, easily explained by someone else's self-interest just happening to align with their own goals.

This should bring you into the right mindset to write the character's reactions without cringing. If it doesn't, consider whether their attitude is truly consistent with their nature and nurture. And the exercise, of course, works with any character; simply adjust the emotional reactions to suit their nature. Once you've done it a couple times, it should be easier to slip into their mindset and consider only the events leading up to the immediate situation, rather than having to start from the beginning.