Paper on the Theory of a Codebase

A few months ago, I came across a post here where in the comments, a CS paper was referenced (I believe written by Norvig) roughly about how subsequent programmers in a project will never attain the level of intution about the codebase that the original developers because they hold the "theory of the codebase" in their head.

Does anyone know which post this was or have a link to the paper? I haven't been able to find it.