Most people treat writing as the step after thinking. You figure out what you believe, and then you write it down to communicate it or remember it. Writing, in this view, is transcription — a record of thought that already happened. This is the common understanding, and it's wrong in a way that matters, because it misses the most useful thing writing does, which is not recording thought but producing it.
What's actually true is that writing is how you find out what you think. An idea can live comfortably in your head for years in a vague, unexamined state, feeling complete because nothing has ever made it be precise. The moment you try to write it down in plain sentences, the vagueness has nowhere to hide. The gaps you'd been gliding over become visible, because a sentence forces a commitment that a thought never does.
This is why writing is uncomfortable, and why people avoid it even when they're good at it. It's not the typing that's hard; it's that writing exposes the parts of your thinking that weren't actually finished. You sit down sure you understand something, and three sentences in you discover you don't, that there's a hole right where you assumed there was a foundation. The discomfort is the tool working. It's catching an error your head had let slide.
For a founder this is enormously valuable, because so many expensive mistakes are really just unexamined assumptions that felt solid until reality tested them. Writing tests them earlier and cheaper than reality does. A decision that seemed obvious in your head will often fall apart when you try to write the reasoning down, and falling apart on the page costs nothing, while falling apart in the market costs the company. The memo is the cheap version of the lesson.
There's a reason the best-run teams tend to write their decisions down rather than just discussing them, and it's not about having a record, though the record is nice. It's that the act of writing forces the thinking to be real. A discussion rewards whoever's most confident and articulate in the moment. A written argument has to survive being read slowly, by a skeptical person, with time to find the weak link, which is a much harder and more honest test.
The forcing function works at every scale. A one-page memo will expose a weak argument faster than an hour of conversation, because conversation lets you patch holes with tone and momentum and the listener's goodwill, while the page just sits there with the hole in it. If you can't write the case for a decision clearly, that's not a writing problem to fix later. It's a signal that you don't yet understand the decision well enough to make it.
This reframes writing from a chore into one of the highest-leverage things a founder can do with an hour. Not writing to publish, necessarily, or to impress anyone — writing to think, in private, badly, just to find out where your reasoning actually breaks. The output might be a paragraph nobody else ever reads. The value was never the paragraph. It was the discovery, forced by the writing, of what you actually believed and where it was hollow.
So the test for whether you understand something is whether you can write it down clearly. Not say it — saying is too easy, too forgiving of vagueness. Writing it. If the sentences won't come, or come out tangled, the problem usually isn't your prose. It's that the thought underneath isn't finished yet, and the writing just told you so, which is the most useful thing it could possibly have done.