The rule simply states that the success or failure of your program depends: 40% on the audience, 40% on you, your product, and your offer. including the value proposition, and 20% on creative and format, including ideas, copywriting and design.
Turning these obvious thoughts around, you will succeed in performance / direct marketing if you effectively communicate the right product with the right offer to the right audience.
Consider this: You will never sell a Medicare-supplement product to an audience of 18 to 49 year olds. It is equally unlikely that you will sell a term-life product that issues up to age 59 to anyone in the retired market. So much for the importance of audience. Copywriters need to know their audience.
Your copywriter is justified in assuming that the product you have asked him or her to work with is the “right product.” On the other hand, any copywriter worth his salt will tell you when your product is wrong. That leaves the copywriter with the right offer to effectively communicate to the right audience.