I'm an only child and I have an only child. (None of this by choice)
As a child I would hear from other children:
"You're so lucky" when in fact, I was terribly, terribly lonely.
"You get so much." when in fact, my father was a factory worker and we had very little.
As an adult, I hear people talk about only children when they don't know I'm one and my daughter is one. "That's probably because they were an only child" is common for any one of a number of negative qualities another person might have.
People think I talk alot and my daughter talks alot. They don't understand the pressure to "perform". At the dinner table, you're the source of your parents conversation.
I notice how freeing it is for my husband, the oldest of six to "disappear" at a family gathering. No one misses him for a moment. An only child can't disappear.While never saying so, I sense that when I tell someone I'm an only child, they assume I'm selfish. Research shows the opposite about only children.
I realize and appreciate the some of the positives of being an only child. It's hilarious, however, when my only child daughter and her only child boyfriend and I get together. Everyone talks over everyone else. I think that's becasue we were called upon to always keep things going - a big job that isn't always welcomed by friends and spouses.