Why does somebody don't like to have siblings?

I was an only child until a month before my 31st birthday, then my Dad and Stepmum had a daughter. I was happy to have a sister at last! Because I was an only child myself, I chose to have a large family of my own and had four children. I think they would be happier as only children though, as they often fight and argue! I guess it is human nature to want what we haven't got - "the grass is always greener on the other side"!!

I think this people doesnt know that having siblings is so much fun. I have students who are already 10 years old and I always ask them if they want to have a younger brother or sister and they said they dont want to cause they just want all the love and attention of their parents to be only for them and not with someone else. I wonder what's making them jealous when in fact they already have all the love they want and they can actually just share.

the main reason might be their environment where they have grown. There may be liking of one more than other by their parents. Usually this is seen only with 2 sibilings...