Unless you assume that everything/anything is a constant, stochastic processes are everywhere. They happen to be used a lot in finance and physics, since real w

Unless you assume that everything/anything is a constant, stochastic processes are everywhere. They happen to be used a lot in finance and physics, since real world phenomena can be intuitively modeled as a random process, in contrast with deterministic models. If you're interested try googling "stochastic processes in [insert field]".