You seem to think of writing simple programs used only by myself (and people I have a relationship with, and people who want to have a relationship with me) as

You seem to think of writing simple programs used only by myself (and people I have a relationship with, and people who want to have a relationship with me) as some sort of special situation that doesn't require "good engineering practices." I think of it as the most basic situation of all. The most foundational engineering practice of all: tailor interventions to the context.