Few minds wear out; more rust out.

Related:

• There are few wild beasts more to be dreaded than a communicative man having nothing to communicate
  Christian Nestell...
• Affliction, like the iron-smith, shapes as it smites
  Christian Nestell...
• The small courtesies sweeten life; the greater ennoble it
  Christian Nestell...
• It is better to wear out than to
  rust out...
• The cheerful live longest in years, and afterwards in our regards
  Cheerfulness is the off-shoot of goodness. -- Christian...
• Life is to the universe as rust is to iron. We are
  in the final judgement (on a planetary scale, certainly)...
• One who is contented with what he has done will never become famous for what he will do
  He has lain down to die, and the grass is already over...