I'd like to take a moment to talk about common problems with car paint from the stuff you can't see to the thing you can.
Since the mid 1970s, most cars follow the diagram to the right. By which I mean there's three layers on top of the body panel, primer, base coat and then clear. Prior to that, it was primer and color, no clear.
The Paint Surface
Because of the color of your car, sometimes you see these defects and surface containments and sometimes you don't. Darker colors, like your blacks, grays, blues etc, show the defects like scratches and swirls. Lighter colors, silvers whites, light grays, show the containments like iron deposits, over-spray. Think contrast in color. If you're not on you knees washing your car, you most likely not going to notice the tar along the bottom edge of the door on a black car.
Over-spray is simply someone spraying something liquid, you were in the area with your car and whatever was being sprayed ended up on your car. Maybe you passed under a bridge and they were painting, as much as they try to cover up and contain it. Or you were in a parking garage and they were painting on another level.
Brake Dust and Rail Dust
Iron Removal in action
Brake dust is an easy one. It's just the breakdown of your brake pads from rubbing against the rotors on your car. Most of it just gets thrown around the barrel of your wheels. Some makes it to the road you drive on, gets kicked around and up into the air and onto your car. It builds up with all the dirt from driving so its on every car.
Rail dust is a term used to describe the iron or rust that gets on the car from being transported on trains. It's from the friction between the wheels on the train and the rails. It also comes from the rotors on our cars as they wear down.
Rail dust is easily visible on light colored cars, especially white. Just look for the little orange spots.
Used more as a general term for anything floating in the air that can end up on your car and sticking to the paint.
Stuff like this you probably can't even see but its there. A quick little trick for you. After you've washed your car, take a sandwich baggie and put it on your hand. Now run your bagged hand over the paint. The baggie will amplify things that are setting on the paint you can't see and you'll be able to feel them.
Self-explanatory. Comes from anything that can cause a deep gouge into the clearcoat/paint. These can obviously range from shallow, barely into the clearcoat to into the paint, through the paint or right down to the metal. Heartbreaking, discouraging to see. Depending on how deep will determine if the scratch can be eliminated or made less noticeable.
Swirl marks are also one of those things that is more noticeable with darker colored cars. Just ask anyone that owns a black vehicle. Swirls are caused by a combination of improper washing, drying, and car washes. Yes, even that touch-less wash can causes swirls.
Less noticeable on light colored vehicles but still there.
Acid Rain/Bird Droppings
These two can also leave permanent marks on the paint surface. Left unchecked, they can etch into the paint. Though, these can be prevented from causing any damage if noticed soon enough and cleaned off.
All this issues help to dull the finish on your car's paint. Instead of the light hitting the paint and bouncing straight back, the light is being defused as it's bouncing off all these paint defects.
All these common paint issues can be fixed though. All are case by case as no two cases are the same, IE scratches of different depths, a shallow one could be polished out but a deep one can only be diminished.
The first three, over-spray, brake dust, industrial pollution, can be removed with clay bar or some cleaning chemical. In some cases, a light polishing might be required but totally fixable.
Scratches, swirls and any kind of etching from acid rain, bird droppings or sap, all require some form of polishing. Some more aggressive than others. Some required multiple steps to repair, heavy buffing then maybe a couple different levels of polishing. If it can't be removed, it can be made less visible.
All in all, most paint can be cleaned up and brought back to like new condition.