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

I suppose that they want others to experience the pain that they are feeling. Sometimes, when people are hurting it hurts even more for them to see those around them doing better than they are. Often times, people want to see you do good, but never better than them. Sometimes these people are not truly aware of what they are doing, or they simply do not care. I think people can get to a point where their actions are unlike who they really are inside and what they would normally do, simply because they're in pain and they're depressed. I feel that it shouldn't be taken personally when people do that, but it can also be toxic and a good idea to distance yourself from the person. It's a realization that they have to make on their own, because if they are already in pain and inflicting it upon others, pointing that out may just upset/anger/hurt them more, causing them to inflict more pain upon you or others that they encounter. However, I'm no professional. :) If this situation is personal to you, I truly hope that things begin to look up for you. xx

Because a person in pain wants nothing more than to soothe their own, and seeing others suffer the same thing helps. Also, a person in pain wants others to understand him.

People who are in pain usually lash out at others because they are miserable and/or angry and people who are miserable and/or angry usually feel a loss of control. Inflicting pain on others does 2 things for them: 1)it allows them to make others feel as they do (yes, misery does love company) and (most importantly) 2)it provides them with some sort of sense of control. If you are on the receiving end of their pain, it usually helps to acknowledge that they are in pain but that you don't appreciate them projecting on you. Stand your ground and let them know that you would be happy to help them any way you can, but not if they continue trying to hurt you mentally, physically, or emotionally.

Because they want others to feel the same way as they are. They want them to know what they are going through.

People often want others to feel the pain that they do. They feel it's unfair that they alone have to suffer when everyone else is smiling and laughing

I would say that people wish to inflict their pain upon others because they feel as if nobody understands them.

Sometimes pain comes from feeling like you're not in control. Hurting others can be a way to think you have control over something. It's also a way to express emotions people don't necessarily know how to handle. Unfortunately, most people don't realize that this only makes their own pain worse.

Probably because that person is feeling bitter or too overwhelmed by the pain that they can't control their actions and thus take it out on others closest to them.

I believe someone who is already in pain may wish to inflict in upon others so that they do not feel so alone in their pain.

Sometimes people feel that the only way they can truly show others that they are in pain is to inflict that same pain to others. Not that they want others to be hurting as well, but just that they want someone to see that THEY are hurting! And sometimes they don't mean to hurt others, that is simply the only way they have figured out to vent or let off a little steam.