Answer: THE APPEAL.
And more specifically, the appeal as stated by your headline.

I have seen one ad pull as much as nineteen times the response of another. Both ads occupied the same amount of space in the same medium, and both had superbly written copy and graphic design. The difference that made the difference was the appeal. One got it right, and the other didn’t. John Caples

Even if you launch with an “OK” ad and a shitty lander, hitting the correct appeal will make all the difference. Everything else can get dialed in and optimized later AFTER you’ve found what your market wants and responds to.

Moral of the story is split test until your customers react to your offer like this…

…through your affiliate link of course