As long you are a single being, living alone without any human interaction, rules based on values or principles are not exactly a part of your life. But as soon you meet someone else, and you decide to live together, various basic ground rules become important to keep the peace.
"I love you." Most of the time, when this sentence is spoken, written or heard, it is used by a person who wants to express a strong, intense feeling of attraction, often infused with passion and desire for another human being.
As no-one is born with a fixed set of opinions, they must have been grown. To understand the origin, it is needed to dig down to the roots of your beliefs.