There are advantages to being an only child, or raised like an only. (My next closest sibling was 12 when I was born.) But there are also things you miss out on, and like anything, you're left with little clues about yourself.
I am thinking of this because a friend was telling me about the child of a mutual friend, who is growing up as a "like an only," similar to the way I was. She LOVES to play hide-and-go-seek whenever they're together. Even at "her age" -- 8.
I told her I completely understood. Because there are tons of games you can play by yourself. Checkers. Solitaire. Even monopoly. (You can even cheat yourself.) But hide-and-go-seek just doesn't work unless you're Sibyl.
Mine wasn't hide and go seek. It was seesaws. Whenever we went on a vacation, my parents would stop at playgrounds and let me play for a bit. They were older, so they'd sit and watch while I played.
You can swing by yourself.
You can slide by yourself.
You can't seesaw by yourself.
Once I had two kids, I bought a seesaw.