You Know, But Can You Articulate?

I was in an interview and got asked the difference between a type and an interface in TypeScript. Not a trick question, not even a hard one. I use both constantly. I know exactly which one to reach for in a given situation without thinking twice about it. And when the question landed, my mind went completely blank, not because I didn't know the answer, but because I had never once had to put it into words. It just lived in my hands, not my head.

That gap bothered me more than the question did.

There's a specific kind of confidence that comes from doing something enough times that your hands know it before your head does. You read a stack trace and you're already three steps ahead of your own explanation. You look at a schema and something in you goes "this is going to bite us in six months" before you can say exactly why. It feels like knowledge. It behaves like knowledge: it gets the job done, over and over. But it's not the same thing as being able to hand that knowledge to someone else.

I used to think articulation was just a communication skill, a nice-to-have layered on top of the real work. I don’t think that anymore. I think the inability to articulate something is a signal. Sometimes it means you understand it so deeply that it’s become instinct, and sometimes it means you never actually understood it, you just pattern-matched your way to a working answer. From the inside, those two states feel identical. The only way to tell them apart is to try to say the thing out loud, or write it down, and watch where it breaks.

That’s the uncomfortable part. Articulating isn’t just translation. It’s a test. It’ll expose the places where “I know this” was actually “I’ve seen this before and it worked out.” And the more senior you get, the more those two things get mistaken for each other, because you’re rewarded for the output, not for whether you could defend the reasoning.

So lately I’ve been trying to actually explain the things I think I know. Not because I suddenly care about being great at technical interviews or writing documentation, though that helps too. I just don’t really want to find out again, halfway through a question, that something I thought I understood only made sense as long as nobody asked me to explain it.