here are the problems:
a) you get all the attention form you parents all the time -> high chance you become a diva when you are grown uo
b) you dont have to share stuff with you sibling -> high chance you become a selfish person when you are grown up
c) you dont have to fight with your sibling over something -> high chance you become a weak pussy
a) Not a diva but getting all the attention from my parents was good as a little kid but bad later especially with school and exams as they always pressuring me and scrutinizing like everything I did.
b) Sort of true, I don't like sharing my stuff but i'm not selfish per say but sometimes I can be absent minded when it comes to other people as i'm not used to sharing.
c) Don't think this depends so much on having siblings.
fair enough. I know a lot of only children and I would say that 75% of them tick at least box a) and b).
thats my personal experience. but I also know only children who are the exact oposite.
I think what kind of person you become as an adult depends on many different things, siblings (or the lack hereof) is one factor. one of many.