While the engine is central to your car's operation, it's the vehicle's bodywork that people see while you're on the road. The paint finish on your car is designed to serve two purposes. First, it provides a surface coating that protects the substrate metal from rust, corrosion, and other outdoor elements. Secondly, it also serves a decorative purpose, giving your car that attractive look that made you purchase it.
That said, your car's paint finish isn't designed to last forever.