My mom taught me many things, but two that have served me well are: Always send a thank you note, and refill the ice cube tray after you use it. Many folks have overlooked my transgressions because I practiced these simple courtesies.
Expressing the sentiment of appreciation is difficult. Gilbert Keith Chesterton tells us, "The expression of thanks is the highest form of thought." We are forever in debt to those who are kind to us.
Further, a sense of entitlement is the antithesis of gratitude — it's a form of hubris that places us as the center of the universe where everything is judged on the basis of its effect on us. When you think that the world owes you, any simple courtesy becomes your just due. The Old Testament Writers in the Book of Psalms tells us, "Goodness emanates from a fear of the Lord." To fear the Lord is to know your place in life, and when you know that place you become thankful for it.