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The big advantage of metal as good conductor does not come into its own until a closed loop, a so-called electric circuit, is formed. In such a loop the highly mobile electrons can constantly be moved around without producing any piling up of charge carriers with positive or negative polarity at different locations and as a consequence any back driving forces.
To maintain a constant flow of electrons, the same number of electrons which enter a certain volume element per unit time have to leave this element. Only under this condition no piling up of charge carriers will occur and a dynamic equilibrium or stationary state can be maintained.