A boy 'n a girl were playing together. The boy had a collection of marbles. The girl had some sweets with her.
The boy told the girl that he will give her all his marbles in exchange for her sweets. The girl agreed.
The boy kept the biggest 'n the most beautiful marble aside 'n gave the rest to the girl. The girl gave him all her sweets as she had promised.
That night, the girl slept peacefully. But the boy couldn't sleep as he kept wondering if the girl had hidden some sweets from him the way he had hidden his best marble.

Moral:
If you don’t give your hundred percent in a relationship, you’ll always keep doubting if the other person has given his/her hundred percent.