A lot of research has been done about pain and how people cope with it. One thing that researchers have found is that many people who have chronic pain who do not cope well often have other issues besides just the pain.
For example, some people have a personality trait called Harm Avoidance. While it is perfectly natural to want to avoid situations that might cause harm or pain, some people take it to the extreme. They can worry that certain things may trigger the pain, become very stressed and fearful. This stress and fear can often become more debilitating than the initial pain itself.
This is not to say that people who feel a lot of pain have personality disorders, but it does explain that certain people who have certain personality traits can be more susceptible to the pain and this can result in other issues that also cause discomfort.