What does the metaphor eat away?

The metaphor "eat away" typically suggests a gradual erosion or destruction of something, often referring to emotional or psychological states. It conveys the idea that an issue, such as worry, guilt, or regret, slowly diminishes a person's well-being or peace of mind, much like how corrosion eats away at metal. This imagery highlights the insidious and often unnoticed nature of such internal struggles.