I would say it's the same thing that makes anyone good at anything: The ability to take the body of knowledge associated with the field and not only synthesize

I would say it's the same thing that makes anyone good at anything: The ability to take the body of knowledge associated with the field and not only synthesize it, but to riff on it and make new -- or at least -- compelling things. That might be too broad. Specific to UX, I would say that many companies only consider what a user experiences and the stories they accumulate when their brand is mature -- usually much too late to pivot. A good UX designer in an early stage venture is usually also an interface designer, to some degree, and taps into the following: 1) Deep understanding of the market and demographic 2) A solid grasp on what people expect 3) A great appreciation for the things that compel people to action UX designers and engineers make things that cause people to accomplish goals in a way that is unobtrusive (except when it needs to be) unoffensive (except when it needs to be) and not confusing (ever). That's my take, at least.