In metal bodies, an electromagnetic wave excites vibrations of free electrons and transfers all of its energy to them. The vibrating electrons emit electromagnetic waves and form reflected light. In dielectrics, electrons are firmly bound to their atoms, the amplitudes of their forced oscillations under the influence of electromagnetic waves are much smaller, and therefore they reflect light weaker.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.