Family Love

How can anyone be expected to love everyone leave alone everyone loving everyone. That's what the family is about. That why I find it amazing how the system still works. In the subdued world it was quite easier to work - but now with the people gaining more freedom of opinion and voicing their choices. Still there are functional extended families in existence today. Why/How does that happen? This questions stumps me.. if you think you know the answer do let me know..