In the Hardy-Cross method for pipes, why do you have to guess flows first and then keep correcting them?

The Hardy-Cross method for pipes is an iterative technique used to determine the steady-state flow distribution in complex, interconnected pipe networks. The necessity to guess initial flows and then iteratively correct them stems from two fundamental principles governing fluid flow: the conservation of mass (continuity) and the conservation of energy. The conservation of mass dictates that the sum of flows entering any junction must equal the sum of flows leaving it. The conservation of energy requires that the algebraic sum of head losses around any closed loop in the network must be zero.