When something is hard to believe or comprehend usually it needs to be demonstrated. For example, when a new technology is introduced on the market it is usually presented to the public through a demonstration of its functions and usability. Sometimes, to truly understand the logic behind a phenomenon or a concept, people need to see not just the result; they have to understand the functions and process that caused the observable result.
Complex processes and functions can prove really hard to explain solely through text, or they can be difficult to put into words. For the uninitiated, a Chemistry class demonstration without any explanations could seem like a sorcery lesson. Even if the reaction is described through a number of pages, some will have difficulties understanding what happens at a molecular level.