From Sidney Harris,
http://www.sciencecartoonsplus.com/originals2.html, see also
http://astro.wsu.edu/worthey/astro/html/lec-cartoons.html
Actually, in everyday life the distinctions between wave and
particle behavior are seldom observed directly, which is why the
concept did not become firmly established until early in the
20th century. Then, it was found that not only light but the
fundamental particles such as electrons and protons also have
wave-particle duality, resulting in behavior that can only be
described by the branch of physics called quantum mechanics.
Once the theory was established, it was found to unite and
explain a huge number of things that do have everyday
implications. An example coming up soon is the structure of the
atom and why a given type of atom emits and absorbs light only
at very specific wavelengths.