I think the most difficult concept to teach people about containerized development is that it's basically another computer.
You can't set an environment var on your MacBook and have it available in your Docker container. You have to be explicit.
Come to think of it, boundaries in general are difficult to get a grasp on—why you want them in the first place, vs. installing all dependencies into one context (your computer) and struggling with the interplay between everything you've installed.
More queer, more garden.