Copywriters need to know how to write. Art directors need to know how to design. Trust me on this one, I didn't make it up.
One of the things I hear from a lot of recruiters and older creatives is that students and juniors don't know the craft. Writers don't know how to write. (Or spell.) Art directors don't know how to lay type, using any program but Photoshop, etc)
It's one thing to know how to concept, but you also need to know how to execute. (And sometimes your job is more about the executing than concepting)
What am I writing about again? Oh! Yes! How to write a newspaper ad.
The Newspaper Association of America (Yes, this exists. And yes, people still read the paper. Surprising, I know!) had a few big names in the ad world write ads about making ads. (How meta)
(side note: if you don't know who these people are, google them immediately.)