A variable flow resistance system for use in a subterranean well can include a flow chamber having an outlet and at least one structure which resists a change in a direction of flow of a fluid composition toward the outlet. The fluid composition may enter the chamber in the direction of flow which changes based on a ratio of desired fluid to undesired fluid in the fluid composition. Another variable flow resistance system can include a flow chamber through which a fluid composition flows, the chamber having an inlet, an outlet, and a structure which impedes a change from circular flow about the outlet to radial flow toward the outlet.