Why would someone who is already in pain wish to inflict it upon others?

I believe that someone who is already in pain is blinded by their own emotions and so unable to understand or feel for others. Their minds are so cluttered with negativity that they believe they are the only ones who suffer from sorrow in their lives. They believe they are alone and have no one to help them. Because they believe no one is looking out for them, they may develop feelings of envy and hatred against others. They begin to believe that life is unjust and that they should not be the only ones who are suffering leading to strong feelings of inflicting pain on others.

Someone who is already in pain might wish to inflict it upon others because some feel that if they bring someone else down, it will bring them up. While this is often not the case, some will continue to hurt others in order to feel better about themselves. Some feel that if they hurt others in a way that they are not hurting, they are better because they are not feeling the same pain that person is. People usually want to feel like they are better than others, because of this they will do anything they can to bring themselves up. This is not the case for everyone, though.

Some people are just built like that. They believe that what they are going through is horrible and has ruined their life or they may feel angry at other for being able to live painlessly and thus want to make others feel that pain. Therefore by choosing to make other feel pain, they can feel joy or happiness or some kind of solace at knowing that they are not alone and others will suffer just like them. Or they might make others feel pain, so that they too can become just like them. If someone wishes to do this, to others, they should receive the help that they need.

Sometimes, people may want to get back at the world for the pain inflicted on them, or struggle to process their emotions in a healthy way, and their desire to inflict pain upon others could possibly be a coping mechanism. Maybe this person struggles with intrusive thoughts or desires, and does not know how to handle these thoughts or desires, and need help perhaps through therapy, apps like 7 cups, mindfulness activities or other activities which can increase a person’s mental well-being and health. Sometimes, they may want a reaction out of the person, due to loneliness. They should be supported.

It's the perceived passage of pain. Someone selfish who's hurt needs everyone around them to hurt too. Then they feel that others can empathize with them, when in reality, they are just isolating themselves.

To find a way to cope with what they're going through. I'm not at all saying that it is okay, but that's how some people decide to handle things.

For revenge maybe. People may have no answers and blame it on others. Not their fault, maybe they just aren't so good at handling pain

Because they are putting their anger onto others. It is an unhealthy mechanism of coping with pain..

Someone who is in pain don't have healthy ways to cope with that pain. They don't know how to deal with it in an appropriate way so they are wishing it upon someone else to be sure that there is someone that is going through the same thing as them

They might feel that others who have wronged them deserve punishment for hurting them. Or they may feel that they are alone and become envious of people who seem to be having it easy, and believe that they should suffer too, even if they haven't hurt them.