Hey,
I can't write for shit regardless if I read x y z book. Does that automatically mean I won't succeed in affiliate marketing? Is it a MUST that I need to know how to write my own copy? Is there ANYONE out there that just hires people to write some compelling copy / advertorial ? Is there hope for me in that aspect? or do I just really need to learn how to write copy?
Writing is like any other skill. The more words you dump on the page, the better you'll get over time.
If you feel like you struggle to grasp copy (or dont' really want to learn it), I would suggest hiring someone to do it for you. It's a craft that some people love and have developed the skill in.
If you wan't to learn to do it yourself, take a pen and paper - (yes, a pen and paper, not Word) and hand write these letters.
I wouldn't say it's a must you need to know how to write it, but you do need to be able to recognize good copy, understand why it's good, and reverse engineer it.
You don't need to re-invent the wheel or create totally fresh/new copy, take what you see working and iterate on that, get data on if it helped/didn't help, and keep going.