Don't invent a cause until you can name the gap.

Something arrived. You did not get to rerun it. A story is already forming.

Gap Last is a way to stay with what happened long enough to name what is still unknown, and only then invent a cause. The formal name is constraint-first reconstruction. You can use the Gap Last method without reading a paper. A working draft of that paper is here if you want the longer argument.

Say what happened as tightly as the evidence allows, and mark how sure you are. Use what is already known, fully: the geometry, the timing, what the record can and cannot show. Name what is still unknown, as a question. Only then propose a cause, and only for the question you named. When better evidence arrives, expect the question to move, and let it.

This exists so the next warning system, the next treatment, the next fix aims at the right object. Someone will build those on whatever cause gets written down. A cause aimed at the wrong object leaves people as exposed as before, with the added harm of believing they are not.

Pursue the how at your folly if you fail to frame the correct what.

Four lines, no tool required

1. The what, as tightly as you can say it. Mark it.
2. One mechanism the geometry, timing, or record already eliminates.
3. The leftover gap, named as a question.
4. Whether how or "who caused it?" is even the right question yet.

The Gap Last method · Run the skill · GitHub

Do not start with who caused it

If that is the first question, reconstruct first. The prohibition is the product.

A parent, a patient, a founder, and an agent meet the same shape: something arrived, you did not get to rerun it, and a story is already forming.

The week that named this is a late-August 2026 flood off Langtang Lirung. The Gap Last method is what happened there, written down so it can continue to happen on purpose, and so the next warning system, the next treatment, the next fix aims at the right object.

The name is Gap Last, not Last Gap. Naming a leftover question is not the same as knowing you have the last one. A later trace can move the question. Treating the gap you named as closed, when you do not yet know enough to say so, is the same thin move the method exists to stop.

It has an older relative. Chesterton's Fence says find out why the fence stands before you clear it away. Gap Last stands on the other side of that fence: name the gap before you build one. Both refuse a cause invented ahead of the question.

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