You cannot compress water. Put a glass into another glass filled with water and the water will come out. If the water can’t come out then the glass will not slide inside the other glass.
Our lungs have a pleural lining that surrounds them and the inside chest wall has one too.A small amount of surfactant is a lung fluid that is between those two pleural linings. Much like taking two sheets of saran wrap and putting oil between the two of them. Man they will slide very easily.
So when we breathe the lung tissues slide easily inside the chest wall. Sometimes we get to much fluid between our lungs and the inside of our chest wall.. When we take a deep breath it hurts bad because our lungs are pushing up against that fluid and the fluid will not be compressed.
That fluid can be blood, plasma, surfactant or infection. This fluid if it builds up is called pleurisy. Pleurisy typically causes sharp pain, almost always when you are inhaling and exhaling. In fact in between breaths it doesn’t hurt at all.
The underlying medical conditions that can cause pleurisy are numerous.
So if you develop these kind of symptoms it could be pleurisy: