The phrase kept surfacing all day like a coin that won’t stay buried.

A woman who runs an enormous company said it almost in passing — that when a hard decision lands on her, in five minutes or five days, she reaches for her first principles. I had been hearing it everywhere for months, said the way people say a password, with a small confident nod, as if everyone already knew what was behind the door. I nodded too. And then somewhere around the third matcha I admitted I didn’t actually know what was under the words, and I went looking.

This is the first of six short walks into that question, and they are meant to be useful, not clever — so let me put the plain thing first, because the plain thing is most of it.

Most of the time we decide by likeness. You do the thing because it is the done thing — because it worked before, because the others do it, because there’s a shape already cut and following a cut shape is a relief. That is reasoning by analogy, and it is most of human life, and it is fine right up until the cut shapes stop fitting. To reason from first principles is the other motion: you refuse the borrowed shape and go down instead, asking but why is that actually true under each answer, until you hit something that can’t be broken into anything smaller — and then you build back up from only that. Likeness copies an existing map. A first principle is what you stand on when you’ve walked off the edge of every map.

Aristotle found the bottom of this two and a half thousand years ago, and it’s worth one breath. Every reason leans on another reason — this because that, that because the other — but the leaning can’t go on forever, and it can’t honestly curl back into a circle. So it has to stop. Somewhere there is a starting point that holds up everything above it and is itself held up by nothing. That stopping place is a first principle. Not a thing you prove — it is what proof is made of — but a thing you reach by going down until the why runs out.

And here is the part the confident nodders skip, the part that turns this from a clever trick into something that costs you. The floor where the why runs out cannot be proved either. You don’t arrive at a final, settled because. You arrive at a place where you plant your feet and say here — knowing, if you’re honest, that you are standing on something you chose to stand on. The bottom of reasoning is not more reasoning. It is a commitment. A small, clear-eyed act of nerve. Feynman, who was nobody’s mystic, said the first principle is that you must not fool yourself, and you are the easiest person to fool — and that is the whole danger down there, because the thing most eager to pass itself off as your bedrock is your own wish. A true floor is the one that survives your wanting it to be false.

Which is exactly why no one can hand you yours.

A first principle told to you is just one more borrowed shape, one more line on someone else’s map — a conclusion you are renting. It becomes yours only when you have gone down the shaft yourself and stood on your own floor and felt it hold. Two honest people can dig to different floors and both be whole. Where you choose to stop digging is where the borrowed world ends and you begin. That little leap at the bottom is the most personal thing about you — more yours than your opinions, which you mostly inherited, or your tastes, which mostly inherited you.

This used to be a luxury, a thing for philosophers with time. It isn’t anymore. We are living through years when the old maps are dissolving faster than anyone can redraw them — when the done thing stops being the safe thing, when a machine can print you a thousand routes in a second and not one of them is yours. When the maps go, the only thing left to steer by is a floor you reasoned down to yourself. That is why everyone is suddenly saying the password. They can feel the maps going.

So that is what these six walks are for, and they are practical, because I have had enough of the password. First — the next one — how you actually find your own floor, which is harder and stranger than look inside, because the inside is a crowded room full of voices that are not yours. Then how a floor you’ve found refuses to stay put: how it deepens, and when you are allowed to move it, and when you are only being talked out of it by fear. Then how you stand on one to decide — and why deciding from a principle works where deciding from fear never can. And finally how, over years, the same few stones quietly remake you, and remake the work you make.

For now, only the one plain thing. Under all your reasons, if you go down far enough, the why runs out, and you are left standing on something you cannot prove and did not inherit and would pay for again. I went down this morning and found mine waiting where it has been all along — that the thing I make must be mine, in my own voice, or it isn’t worth making. I didn’t reach it by proving it. I reached it by standing on it until everything else fell away.

That is a first principle. The next walk is how you find yours.