Grind Down Meaning

(idiomatic, transitive) To weaken someone's morale over a long period.

Example: 1997, The Toasters, Don't Let the Bastards Grind You Down
  I'm living in a world where I don't really fit
  Every day walking through the same old shit
  I'm gonna get my gun, gonna get prepared
  I'm not impressed and I'm not scared
  Don't let the bastards grind you down!
  Don't let them grind you down!
  Don't let the bastards grind you down!
  Don't let them grind you down!