It's normal to fight with your significant other, but narcissists can be incredibly cruel and threatening in heated situations.

This is because they cannot see you as somebody they love, and someone who has angered them at the same time.

Something traumatic could have happened in their early life, meaning they didn't develop "object constancy."

Narcissists cannot change, so the best thing to do is to leave and protect yourself.

We're all guilty of saying hurtful things in the heat of the moment. Every relationship has its ups and downs, usually resulting in arguments, but these don't necessarily mean you're going to break up.

When we quarrel with our loved ones, most of us have the ability not to do too much damage. This is because of something called object constancy. It basically means having the ability to still have a positive emotional bond with someone when you are also feeling angry, hurt, or disappointed with them. It also means being able to feel emotionally connected to that person when they are not physically around you.

To most of us, this is a given, and we can move past the little things. However, to those with narcissistic personality disorder, or people who are psychopathic or sociopathic with narcissistic traits, the negative feelings they have towards someone in the moment are all they can focus on.

If you date a narcissist, chances are they saw you as a worthy target, then they love bombed you into thinking they were your perfect match. They target strong, successful people to prey on partly because they like a challenge, and partly because it makes them look good. However, then they start breaking down your spirit with their abusive, gaslighting behaviour, then discard you suddenly and brutally.

People who have been in narcissistic, abusive relationships often describe their partner as having a "Jeckyll and Hyde" behaviour — one moment they are acting like everything is perfect and you are the love of their life, but something switches and a monster appears in front of you who is angry, cruel, and threatening.

According to Shannon Thomas, a therapist and author of the book "Healing from Hidden Abuse," abusive people can switch between Jeckyll and Hyde so easily because they never take any responsibility for their actions. This is also why they are able to move on so quickly from seemingly relationship-ending arguments, sometimes pretending that they didn't happen at all.

"It's that lack of empathy and that lack of attachment that they can just go from one place to the next," she told Business Insider. "If nothing ever sticks to them, if there's no actual remorse, and no guilt of any kind, then its always someone else's fault. I describe them like Teflon, the frying pan, nothing sticks to them, nothing ever really is their responsibility, it's always projected out."

The lack of object constancy in the narcissist's mind means they cannot cope with the idea that the person they are dating doesn't exactly fit into how their ideal mate should look, think, and behave. When they realise the person they are with is human, with faults and imperfections, that's it. They move on to their next mark, leaving the other person confused and heartbroken.

It's not known how someone becomes this way

A well-respected and cited American psychologist Margaret Mahler studied object constancy in infants. In her work she noted that once a child starts to crawl, it begins to understand that it is separate from its mother, and starts to develop a sense of self.

The first object children learn is their mother, and how all the different parts of her — her voice, arms, ability to feed — all belong to the same being. They also learn that when she leaves the room, she will come back again.

However, some children grow up with this part of their development being fragmented somehow. The reasons for this are not well understood in psychology yet, but both nature (genetics) and nurture (parenting) could play a role.

For example, Mahler wrote that if a child's caretaker is abusive, this can result in a defense mechanism in their psychology called "splitting," which could help explain why some people grow up with a lack of object constancy — and then become narcissists with the inability to have empathy for others.

In this situation, the child needs to feel cared for, even though their parent isn't supplying them with that, and so they repress the negative aspects of the "object," the mother, so they can hold onto the positive ones. In the child's mind, the idea of the mother is being preserved and destroyed at the same time.

According to psychiatrist Perry Branson in a blog post on Psychology Today, this can result in dissociation from the situation. This can happen in adulthood when the narcissist is under stress, such as being in an argument with their significant other. They dissociate from the positive feelings while they are experiencing negative ones and vice versa, seeing the other person as all good or all bad. It's similar to how a toddler has a temper tantrum.

Therapist Perpetua Neo told Business Insider that the behaviour of narcissists in abusive relationships is so insidious that the victims stop respecting themselves. Narcissists can never change, she said, and the best thing survivors can do is run far away from them as fast as they can.

"You want to make sure you reclaim your life in a different way. When you're with a narcissist, you stop doing things for yourself because they don't like you doing things for yourself," Neo said. "Be really clear in your head that this person is a narcissist and really nothing can be done about it. The only thing you can do about it is to take care of yourself."