The difference between deceptively simple and deceptively complex

This is just something I’m noodling about. Sometimes you have a story that appears ridiculously simple when you first look at it, but then you peel back the layers and it suddenly has all this stuff going on and you could write a book about all the different things. And sometimes, you have a story that looks like it’s got a million bells and whistles and layers and wheels going around each other at odd angles – but when you look past all of the surface complication, you’ve actually got a super simple story.
I guess Ex Machina is an example of “deceptively simple.” It’s just two guys and an A.I., in a bunker, but wow there’s a lot going on. And Lost is an example of deceptively complex: It’s got the Others and the Dharma Initiative and a billion subplots and polar bears and everything, but in the end it’s just a story about the Smoke Monster’s sibling rivalry with Lucifer from Supernatural. Or maybe about Jack navigating the conflict between science and faith, I guess.
I have a feeling my stuff errs on the side of “deceptively complicated.” I write things that have a million things whizzing around, but they boil down to one or two simple ideas. Or at least, I hope that there’s one or two main ideas when you look past all the fancy whizzbangery on the surface, or else you are left with just a mickle of a muddle. Right?
I wish I knew how to create something deceptively simple. I have a feeling it’s a matter of keeping the obvious stuff in the story down to the minimum – only a few characters, relatively few locations, a simple plot, not a ton of random plot devices or whatnot. But then letting the characters have complex inner lives, and lots of interesting ideas among them, and a bunch of themes that come up in different ways.
But if something is deceptively complex, how do you keep it from becoming just straight-up overcomplicated and messy? I wish there was a magic bullet – but I think part of it is that if you want to be able to strip away all the layers of complexity and find something stark underneath it all – a single stark element – then that needs to be there the whole time. You have to have one idea that you keep coming back that underpins the whole thing.
So maybe the thing that makes complexity “deceptive” is a having a through-line – an idea, or a story element, that you follow from the very beginning of a work right until the end. At least, that’s one way to tell if it’s possibly working. Maybe.