How is the notion of Lie Bracket related to controllability of nonlinear systems?

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Let there be two vector fields $f$ and $g$ such that $\dot{x}=f(x)+g(x)u$. I know the controllability matrix of this generic affine in control system is given by $C=[f,[f,g],[f,[f,g]],...]$. I want to understand the intuition behind this definition. I am familiar with the notion of Lie bracket and how it measures degree of commutativity of two vectory fields. However what I do not understand is how the notion of Lie brackets is intricately connected with the notion of spanning entire mannifold? Please suggest valuable insights. Thanks for you time and consideration.