Answer: Graphic Design Knowledge/Experience
But wait, most people would think graphic designers are all the same. Nope Graphic Designers are NOT all the same.
I'll make it very simple. It's like saying ALL CHEFS ARE CREATED EQUAL. You know that's not true. Can a French Cuisine Chef prepare an assortment of Sushi the same way a Sushi Chef could? Not unless they were trained to. With graphic design it's the same thing. A designer that was trained and educated in designing beautiful web pages doesn't mean he/she knows anything about marketing and logo design.