---
title: "A New Feature Can Reveal an Old Assumption"
canonical: https://dxdev.com/blog/2026-02-27_new-feature-reveals-assumption/
datePublished: 2026-02-27
---
A new request often exposes rules that were always present but never tested together in the old workflow.

## The practical check

Treat a surprising failure as a question about the underlying model: what assumption did the new feature force into view?

## Where AI fits

AI can trace a new failure back to previously untested assumptions or invariants and prepare the questions that would test whether those assumptions still hold.

## The human decision

People decide which assumption to change and verify that the repair does not break other valid cases.

## The lesson

A new feature is useful evidence when it exposes an old assumption that needs to be tested against the full range of valid work.

That feature-triggered invariant check is worked through in the Build Log companion.