"I believe that no characteristic is so distinctively human as the sense of indebtedness we feel, not necessarily for a favor received, but even for the slightest evidence of kindness; and there is nothing so boorish, savage, inhuman as to appear to be overwhelmed by a favor, let alone unworthy of it."
The mind becomes accustomed to things by the habitual sight of them, and neither wonders nor inquires about the reasons for things it sees all the time.