[sageframe]

You used to know how the application worked because you'd written every line—ground-truth knowledge. Now you know how it works conceptually but there's no source-level backing. Your mental model is abstract, not structural.

That changes the failure mode. Before, the bottleneck was speed—you understood everything but couldn't build fast enough. Now it's judgment—you can build fast but you can't always tell when something's wrong.

The documentation habit is you compensating—building external ground truth to replace the internal ground truth you lost. Which is not regression, but it's also not nothing. A calculator offloads computation. This offloads the knowledge that tells you when the computation is wrong. Different thing.