Persistent pain lasts beyond usual healing times. It used to be thought that this is due to ongoing damage, but scientific research has shown that this is unlikely. The pain is more likely to be related to the nervous system (brain and nerves) becoming sensitised, a bit like the volume on your radio being stuck on loud. When this happens, it can be difficult to do your normal activities. It is possible to turn the volume down, but it takes time and effort. This means that quick fixes, such as medications, injections and operations are often unhelpful.
The reason these interventions can be less helpful is that the nervous system takes short cuts to improve efficiency. This is affected by past experiences, thoughts, expectations and emotions, not only tissue damage/injury. A good example of this is someone with low back pain, where bending the back causes pain. To improve efficiency, your nervous system predicts that bending your back will hurt, even if you are not receiving pain messages from the structures in the back. This is not a conscious decision and is completely normal, although it may be unhelpful in many circumstances.