You stepped on a nail! Ouch!
The alarm in your foot goes off. It sends a danger message to your brain. The brain produces pain to get your attention, so you take care of the problem. If you could graph it, it would look a little like this. Mind you, I'm no artist.
You take care of the foot. Clean it, bandage it, get a tetanus shot. It's sore for a few days, but the pain goes away, the alarm goes down, ready for the next adventure.
In one out of four people, however, the alarm doesn't go down. It remains extra sensitive.
If pain persists longer than the normal healing time for a tissue, it's considered chronic pain. If you cut your finger (or go back to the nail in your foot), you expect it to be sore for a few days, but if you're still hurting weeks later, it's considered chronic pain. Those tissues should heal in a few days.
When pain persists beyond the normal time it takes for tissues to heal, the pain is probably the result of an extra sensitive alarm system. Tissues heal, but the alarm can stay overly sensitive.
So take this to a more pertinent issue--say neck pain or back pain or shoulder pain. When you initially hurt yourself, there was very likely some kind of tissue damage. But we know tissues heal. The body is extremely resilient. Someone with more medical knowledge than me can tell you how long those things take to heal, but somewhere in the range of three to nine months.
When pain persists longer, sometimes years longer, the problem is very likely an extra sensitive alarm system. That sensitive alarm can cause sensitivity in the tissues, pain, and limited movement.