Here's why:

* Oxidation is the process of losing electrons. Metals have a tendency to lose electrons and form positive ions. This is because they have relatively few electrons in their outer shells, making it easier for them to lose these electrons and achieve a more stable configuration.

* Reduction is the process of gaining electrons. While metals *can* be reduced under specific conditions, it's less common in their natural state.

Examples:

* Iron rusting: Iron (Fe) is oxidized to iron oxide (Fe₂O₃) in the presence of oxygen and water.

* Aluminum reacting with acid: Aluminum (Al) is oxidized to aluminum ions (Al³⁺) when reacting with acids.

Key Point: The tendency of metals to be oxidized is what makes them useful in many applications, such as in batteries and corrosion-resistant coatings.