He is ungrateful who denies that he has received a kindness which 
has been bestowed upon him; he is ungrateful who conceals it; he 
is ungrateful who makes no return for it; most ungrateful of all 
is he who forgets it.
  [Lat., Ingratus est, qui beneficium accepisse se negat, quod 
accepit:  ingratus est, qui dissimulat; ingratus, qui non reddit; 
ingratissimus omnium, qui oblitus est.]
 — Seneca (Lucius Annaeus Seneca)
  Ingratitude