From Writers Helping Writers:
Debilitating fears are a problem for everyone, an unfortunate part of the human experience. Whether they’re a result of learned behavior as a child, are related to a mental illness, or stem from a past wounding event, these fears influence a character’s behaviors, habits, beliefs, and personality traits. The compulsion to avoid what they fear will drive characters away from certain people, events, and situations and hold them back in life.
In your story, this primary fear (or group of fears) will constantly challenge the goal the character is pursuing, tempting them to retreat, settle, and give up on what they want most. Because this fear must be addressed for them to achieve success, balance, and fulfillment, it plays a pivotal part in both character arc and the overall story.
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Being Capable of Harm
Notes: Sometimes destructive thoughts enter the mind, causing us to wonder if we are capable of harming others, either as an uncontrolled response because of some internal driver or deficit, or because we become so single-mindedly obsessed about something (a goal, success, power, etc.) we will do whatever it takes to possess it. For most, these thoughts are fleeting, because common sense prevails – I am moral and have good judgment. For others, though, it becomes a deeply embedded fear: I will harm someone if I don’t safeguard against it.
This fear can play out well in storytelling for characters who are unsure where their moral line is, or worry they will lose control of themselves. It can also be a good fear for a villain if you wish to hint at their humanity and whether they might be self-aware enough to be redeemed. Characters with Harm OCD may be especially susceptible to this fear.
What It Looks Like
The character being afraid of their own anger
Warning people away and discouraging relationships
Not liking to be surprised
Intrusive, irrational thoughts about harming others
Acting out a compulsion to push an irrational thought of harm away (repeating, “I’m a good person. I wouldn’t do that,” several times)
Visible shaking
Panicked breathing
Dropping or moving away from the item that triggers ideas of harm
Keeping people at a physical distance
Having only a few close friends or family members
Having to step away when angry
Creating a buffer of space between themselves and others (just in case)
Making an excuse to leave
Avoiding triggers (refusing to watch violent movies, listen to a reporter detail a sexual assault on the news, or be around weapons)
Asking people if they feel safe
Asking people they are with if they believe the character is capable of harming them (seeking reassurances)
Questioning their actions in the aftermath of an emergency, What if I didn’t run as fast as I could have to get help? What if I wanted that man to suffer?
Avoiding being alone with someone who is vulnerable (a child, an elderly person)
Asking for an opinion on a goal, thought, or decision to “test it,” making sure it’s appropriate
Being slow to act because they need to think it through
Hesitating to commit
Avoiding responsibility and not wanting to lead
Being anxious if they want something (from worry over what they will do to get it)
Explaining their actions or motivations to reassure others they are safe
Common Internal Struggles
Having intrusive thoughts on how to get something in a direct, dark way (I’d get full custody if he was dead), followed by shame, fear, or both
An idea forming that it would be easy to hurt someone in a specific way
An impulse to use an item violently (cutting a sandwich at lunch and suddenly imagining using it to stab a family member nearby)
Being irrational: forgetting to return a library book must be a sign they want to deny others the opportunity to enjoy it
Having flashes of violent images
Questioning/worrying they secretly enjoy violence
Constantly examining and questioning their motives
A tendency to magnify small transgressions (bumping someone) and see how dangerous they are (had they been on a subway platform, they would have been pushed into an oncoming train)
Needing to escape situations where anxiety or anger is high before they hurt someone (believing they will)
Mentally reminding themselves of whom they care about and so must be kept safe
Link to the rest at Writers Helping Writers