One Principle Beats 250 Words of Rules
A client's prompt carried 250 words of banned phrases. Every one was banned for the same reason, so eight words replaced the whole list.
The Blocklist
The client had a list. A long one. "Ne jamais utiliser 'il est essentiel de'." "Interdire 'dans le monde actuel'." "Eviter 'il convient de noter que'." On and on. 250 words of "don't say this."
I looked at it and felt the itch. This is whack-a-mole. You ban "il est essentiel de," the LLM writes "c'est fondamental de," same empty filler, different words. You add that to the list. Then it writes "il est crucial de." You add that too. The list grows forever and never covers everything.
The Distillation
I asked Claude to challenge my instinct that this was inefficient. It agreed and went further: the entire 250-word list reduced to one principle.
"Chaque phrase apporte une information nouvelle."
Eight words. Every sentence brings new information. That's it. That's the whole list. Every single banned phrase on that blocklist was banned because it adds no information. The principle catches all of them, plus every variant the LLM will ever generate.
The Broader Thing
The same pattern is everywhere, well past AI prompting. Code style guides with 400 rules vs. "code should be obvious." Editorial guidelines with pages of don'ts vs. "cut what the reader can skip." Team process documents with 50 bullet points vs. one principle people actually internalize.
Rules enumerate. Principles generate. A deny list will always be incomplete, while a positive directive covers cases you haven't seen yet.
~60 words instead of ~250. And it actually works.