This is great advice because it changes the role of the junior from blindly following rules to considering the reasoning before applying a guideline, which over time would (hopefully) lead them to developing their own professional judgment instead of rule-parroting to their eventual subordinates.
Books full of contextless rules also reinforce the meta idea that complexity can always be tamed by simply choosing the right set of rules. Anecdotally, working in environments subscribing to that religion can feel like being intellectually smothered with a pillow.
I teach a lot of programming classes (usually to existing programmers who want to pick up a new skill, sometimes novices), and I tend to word it thusly:
Don’t make me think. I’m not good at it, and I’ll probably screw it up. Thinking is also too much like work, and the entire reason I got into programming was to make machines do the work for me.