Aberrations, or optical imperfections, exist because no lens is optically perfect. Almost all lenses show aberrations from the ‘perfect’ image.
Lateral chromatic aberration
A common lens aberration that produces color fringes around the edges of objects, and an effect that gets stronger towards the edges of the frame. It happens with lenses that can't focus different wavelengths of light (colors) at precisely the same point. These days it can be corrected quite easily in-camera or with software later.