Copywriters are interesting beasts, and have a delicate balance of people to manage when crafting their pitch. Perhaps not everyone can draw, but clients can read and write. It’s not unheard of for clients to come up with alternatives to a Copywriter’s work when they would never dream of doing the same to an Art Director.
The other thing that Copywriters come up against is the notion of simplicity. A Copywriter’s job is to take a whole lot of complex information, and make it easily understandable. To distill pages of text down to just a few words to create a tag line for example, which is neither arbitrary nor so generalised as to have no meaning specific to the product. It’s a specialised skill that takes years of practice to get right. Yet clients may respond with, “I could have written that!”
The point is you didn’t, because if you could, you would have already. Be a good client, and listen to the rationale.
If you’re a Copywriter, you may get inspired by this reference chart created by ABC Copywriting.
Think big, believe in yourself and your capabilities, and back yourself up with strategy and chutzpah.
Good luck!