The reason that corrosion is so common can be seen from the chemistry of metals. Most metals are more stable as compounds than as a pure metal. They have a driving force to move from a higher energy state to a lower energy state.
If you have not already done so, it may be helpful for you to review the section on bonding in materials before you proceed any further.
A common example of corrosion is where the reinforcing steel in concrete corrodes, resulting in cracking and separation of the steel from the concrete.
The economic costs of corrosion are extremely high, with large amounts spent on prevention of corrosion and replacement of corroded materials. It is estimated that 5% of an industrialised nation’s income is spent on the direct costs of corrosion.