No, but my siblings were so far apart from me that sometimes I might well have been - my sister was 14 when I was born, and I was 8 when my brother turned up.
My bother was 16 years older, and my sister 15, so I was as good as an only child, but with the bonus of being well and truly spoilt, especially by my sister and her husband.
I know quite a few only children, and they seem to have been fine. You only have to look at Enid Blyton character George in the Famous Five books to see that one child is enough for some.
I'm an only child. I'm 72 years old, and I never regretted/missed not having siblings. I was quite happy with my own company as a child. My wife has a sister, and they were close as children, but they've drifted apart a bit now, and I don't think that my wife would have minded being an only child. For me, it's never been a problem.
I am the only child of my parents but I do have a half-brother 7 yrs older. He's resented me all my life and thought I was favoured (he was probably right).
I've always wondered if any trials were done to see whether single children had issues with sharing, making friends and were more predisposed to certain traits or lack of compared to children with siblings.
West Korea exists as does east Korea. (I know it's North and South Korea) but I know the the reason for my typo earlier is because i'm on another site talking to someone about directions so got mixed up.