What are the most underrated skills that separate great programmers from average ones?

The key one: slowing down and asking questions.

There’s a tendency among highly skilled people to think that they have a deep understanding of a problem from just a cursory examination and then believe they can just dive right in and start whacking away at a solution

Nothing could be further from the truth.

There are no simple problems. They’re only people that think that there are simple solutions.

Taking the time to talk to everybody that’s ever been involved with this thing and understand the nuances, and understanding the organic nature of how the problem came to be, and understanding the environment in which the solution must be crafted (not just the technical environment, but the political, and financial environment is imperative before you even begin to start crafting a solution.

And you have to have a plan, and an architecture, and a plan for training and handoff and support after the fact in mind if not in place before you write the first line of code

Otherwise, I don’t give a shit how skilled you are as a coder… You have not solved the problem