The Chinese have a beautiful explanation that I really like. They believe that your thumbs represent your parents; your index fingers represent your siblings; your middle fingers represent you; your fourth fingers represent your Life Partner; and your little fingers represent your children.
Try this fun experiment:
Hold your hands opposite each other, fingers open. Bend your middle fingers and hold them together back to back, then join the remaining three fingers and your thumb of both hands, tip to tip.
Try to separate only your thumbs in this position. Your thumbs (your parents) will open, because you are not destined to live with them all your life and usually you will outlive them anyway.
Join your thumbs as before and separate your index fingers (siblings). They will also open, because your brothers and sisters have to live their own separate lives.
Put your index fingers back together again and separate your little fingers (your children). They too will open, because when your children are grown they are meant to move out and find their own way separate from you.
Lastly, join your little fingers again and try to separate your ring fingers, representing your spouse.
You will find that you simply cannot to this – because Husband & Wife are meant to remain together all their lives!