The System Prompt Is Not an Incantation
The system prompt is most often written as an incantation.
Add a "you must," add a "this is very important," add a "please think step by step," then keep trying different phrasings to see which chant coaxes out the desired behavior. This treats the prompt as a prayer to a black box: you don't know how the inside works, so all you can do is swap words and beg.
What Incantation Thinking Gets Wrong
The flaw in incantation thinking is its assumption that the problem lies in the wording. Behavior is off, so tweak a sentence, add another emphasis word. But most of the time, behavior is off not because the chant was recited wrong — it's because the role was never made clear.
Read the same system prompt as an employment contract, and the way you write it changes immediately. It needs to state four things about the role: responsibilities — what to do; permissions — what may be touched; boundaries — what may not; reporting lines — when to escalate, and who receives the work. These are statements about the role, not pleas to the candidate. A good JD does not work because it says "very important." It works because it makes the role itself clear.
How a prompt should literally be written, and why declarative beats imperative coaxing, are model-layer questions (see the first book). This is one level up: using the employment contract to organize what belongs in the prompt. Get the abstraction right, and the anxiety over wording falls away on its own.
If You Can't Write the JD, You Haven't Thought Through the Role
That gives you a simple self-check: if you cannot write a clear JD, the problem is not your wording. It's that you have not figured out what this role is for.
Chanting can mask this for a while — with enough fiddling, you occasionally luck into the right behavior. But a role that was never thought through cannot be patched with emphasis words. Moving your effort from "try another phrasing" to "state the role clearly" is the entire shift from incantation thinking to contract thinking.