What is the 10 rule in essay writing? I heard about it but can't find info anywhere

I was in a study group and someone mentioned "the 10 rule" in essay writing. I asked what it was and they said "you know, the 10 rule" like everyone knows it. I nodded like I understood but I have no idea what they were talking about.

I've Googled "10 rule essay writing" and found nothing. Is it about 10% of the essay being introduction? 10 paragraphs? 10 sources? 10 pages? I'm so confused.

One person said it might be about the "10% rule" for quotes — that quotes shouldn't be more than 10% of your paper. Another said it's about taking a 10-minute break every hour while writing. A third said it's about reading your essay 10 times before submitting.

I asked my professor and she looked at me like I was speaking another language. She said "I've never heard of the 10 rule in 20 years of teaching." So either my study group made it up, or it's something really obscure.

Has anyone here heard of this mysterious "10 rule"? Is it a real thing or did my classmates just make it up to sound smart? I need answers!

If it's not real, I'm going to feel so much better. If it IS real, please explain because I'm losing sleep over this.

The only "10 rule" I know is from my psych stats class — the 10% rule for citations means if you're directly quoting, it shouldn't be more than 10% of your paper. But that's more of a guideline than a rule.

Also someone mentioned Stephen King's 10% editing rule which is legit — cut 10% of your draft in revision . I actually do that now and it helps with wordiness fr.