A conductor is a material where the charges are free to move throughout the material bulk. This results in a self-correcting behavior because if we were to apply a static electric field across a conductor, the electric field separates the negative electrons from the positive (largely) immobile ions in the material. The separation of the charges creates another secondary electric field that will oppose the applied field. The natural movement is thus that the charges will arrange themselves such that no net field exists inside the conductor. Because if there was a net field, more charges would be moved about that would create a secondary field that further decreased the net field. In the end, the equilibrium of no net field is reached.