What a waste it is
to lose one's mind.
Or not to have a mind
is being very wasteful.
How true that is.
- Dan Quayle, US Presidential candidate
trying to quote:
"a mind is a terrible thing
to waste"

Metal that is exposed to oxygen oxidizes in order to form rust. This happens faster in humid regions, or if the metal is wet. Rusted metal shows a form of decay, and it is of a lower quality than before.

Corrosion is another form of decay, in which other metals, not necessarily iron-based, are eaten away, with the result of a deterioration of their quality.

Teeth can decay as well. Although teeth remain in a wet environment and they are not iron-based, that process of decay is different.

a far more significant problem is mind decay. A person's mind is precious, and a mind is a terrible thing to waste.

Unfortunately, many people do not massage their mind sufficiently. They do not take the steps to assure that it will not corrode. The brains with which they were endowed are used insufficiently, so they act foolishly. Many of these people do have the potential for doing wise things, but they or people in their environment have allowed their minds to decay. As a result, they suffer from the decay of a person's most precious possession - his mind.