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

Hurt people tend to hurt others. When a person is going through pain or any struggle in their lives, some have the desire to have another person experience what they’re going through. They do this by putting another person through exactly what they have gone through or what they are going through. Some individuals even do this subconsciously because the pain becomes normal for them. This makes inflicting the pain even more normal for them. This starts a cycle that one person has to work on in order to break the cycle of pain in their lives as well as in the lives of the people around them.