Parable: Integrity is the state

The grandson came home from the store and he happily reported to his grandfather:
- I paid the saleswoman for 10 books, and she accidentally gave me 15. Wasn't that great?
Grandfather frowned.
So you took what you didn't pay?
The grandson was surprised:
- Think of it! Small for her loss.
Grandpa glared:
- It's not her. Let's go back to excess.
When they returned to the store, the boy told the shop assistant that she recently made a mistake and asked to pick up extra notebooks ago. The woman at first surprised, and then warmly thanked and praised the boy, saying he was wonderful and a very honest man and wished him good health and success.
After leaving the store, the grandson was beaming with pleasure. Grandpa asked:
How is it, my dear? Happy? Did you feel that honesty is a fortune? It has to be purchased, and not to waste for a few notebooks.