The concept of a random walk is simple but rich for its many applications, not only in finance but also in physics and the description of natural phenomena. It is arguably one of the most founding concepts in modern physics as well as in finance, as it underlies the theories of elementary particles, which are the building blocks of our universe, as well as those describing the complex organization of matter around us.

Chapter 2, Fundamentals Of Financial Markets, p. 38. - Why Stock Markets Crash - Critical Events in Complex Systems (2003)