The word resistance is the key word here. Similar to how there is a difference between a water resistant and waterproof watch, the same holds true for ceramic coatings. There is no such thing a s a scratch proof coating. Even professionally installed multi-layered 9H type of coatings can be scratched. There is an abrasion test in which pencils of different hardness (1 being the softest and 9 being the hardest) are used to grade how susceptible a surface is to scratching. They use these pencils to scratch the surface to measure how resistant it is to damage. Most automotive clear coats have a hardness of 4-6 on the scale. Ceramic coatings claim to improve hardness up to 9, or 9H. This doesn’t mean that the coating is impervious to scratches, all this means is that it is harder to scratch.