After growing up as an only child, I've only come across one convincing argument for siblings

I'm an only child.

And I'm probably a lot like you think I am. I'm organized and responsible and punctual. I like my space and my privacy and I'm generally cool hanging out alone for long periods at a time.

Hopefully, I'm not as obnoxious or self-centered as you might suspect, but writing an essay on the internet that starts with "I" means my chances aren't great.

Anyway, especially now that I'm watching my friends become parents and dodge the "When are you having another?" question, there seems to be a certain amount of fascination about only children. (Freaks.) If you have fantastic siblings, being an only child probably sounds like a nightmare. If your siblings are the bane of your existence, it sounds like a dream. If your siblings are ... fine, you probably haven't even clicked into this article.

Research tends to come down on the only-children-rock side of things. In JSTOR Daily, Joanna Pocock, mother of an only, writes that 23% of Americans have one child. Sociologist Judith Blake found that only children tend to have better grades and higher IQs than those from large families. Fellow only Rebecca Harrington of Business Insider points out that research has consistently disproved the myth that only children are selfish and spoiled, and that they tend to have better relationships with their parents.

And I can tell you, based on my purely anecdotal experience of my own family and the half-dozen only children with older parents who made up my closest friend group as a kid, it's generally a pretty sweet deal. You get all the resources and the attention and the privacy. You never have to fight anyone for anything, and if you do end up battling a foe, you can leave them at school or a playdate and retreat.

Sure, I would have liked a sibling during a family vacation when I was without anyone to build the other half of the sandcastle, or ... well, actually that's the only time. But as I've gotten older, there is only one reason I've truly, actually wanted a sibling: to have someone else on my team.

Here is my theory (it's a hit with other onlies at the parties where we refuse to share snacks and insist on talking only about ourselves):

When you have two or more kids, you build them their own team: them versus the parent(s). Assuming they aren't mortal enemies, they can cover for each other and pawn off blame on each other and generally represent the kid coalition and the argument for an entire hour of TV after dinner. When you have one kid, you're adding them to the parental team: the three of you - or two of you, if you're a single parent - are a team.

This is no big deal while your kids are little. In fact, it's pretty cool. It's great! It's you guys against the world. But there's a major problem with a team whose members have a 20-plus year age difference: one day, inevitably, the youngest team member will be all alone.

It's not just that your youngest team member will have to care for the older in the most heartbreaking, difficult way. There will be no one to reminisce about Sunday morning pancakes or how Mom always listened to the same three songs in the car. No one will have witnessed the time Dad lost his cool and his face turned that really alarming shade of red and everyone stayed the heck away from the remote control for the next month. No one will laugh at how Mom cried from joy when you got into college or roll their eyes remembering that 12-hour layover in frozen Duluth on the way home from Grandma's after Thanksgiving. There's no one else who was there for the day-to-day minutiae that makes up family life. No one knows a family like the people who are in it.

This theory comes with a few assumptions. First, it assumes your childhood was a happy one and one you want to remember, which is a privilege, not a given. It assumes you and your siblings can be in a room together for enough time to swap stories, and even choose to be there semi-regularly. Again, not a given. It assumes you didn't have another kid filling the sibling space, like a cousin who lived with you starting at age five or step-siblings who witnessed Dad putting chia seeds on his pancakes. What a nut, that Dad.

But, with those assumptions in place, the theory holds true. It's great being on a team, until the rest of your team is gone.

And that's the best argument I've ever encountered against being, or having, an only child.