The following is an interview question from Mark Joshi et al. Quant Job Interview.
Question: Why is Brownian motion useful in finance?
I am from a Pure Maths PhD background (functional analysis, particularly Banach Space Theory). I would like to venture into quant finance industry after my PhD graduation.
Thus, I have no idea on how to answer question above as it seems that most stochastic calculus books would involve talking about Brownian motion but never give motivations.