When two different metals touch in the presence of an electrolyte like moisture, one becomes an anode and corrodes preferentially while the other, the cathode, is protected. The more electrochemically active metal sacrifices itself, so pairing metals of different nobility accelerates decay at the junction rather than distributing it.
Corrosion imposes enormous ongoing costs (estimated in the hundreds of billions of dollars annually in the United States alone) yet remains culturally invisible because it works slowly and unglamorously. An entire specialized profession of corrosion engineers labors largely unrecognized to hold infrastructure together against this constant chemical return of metals to ore.
Smelting forces metal into a high-energy, unnatural purified state, so corrosion is simply the thermodynamic drive of that metal returning to its stable oxidized form found in nature. Viewing rust as metal 'going home' rather than being attacked reframes decay as the default and durability as the costly exception that must be continuously maintained.