I met James around 9 years ago when I was first starting out in professional development, before he eventually joined Mozilla. I inherited more than one massive project from him, and I'd like to assure you he did not actually ignore the form of his code, nor did he avoid improvements that paid huge dividends. I've always been rather OCD about DRYness, and I never had cause to complain about the quality of his work, nor was there ever much of any duplication.

I believe the spirit of what he's trying to get at is not letting concern for DRYness stand in the way of working things out. I saw this in practice many times, and even approach complex projects in much the same way--I'll typically not worry about DRYness until I've implemented something a couple of times, sometimes in different ways, to get a feel for how I can approach it best. Once I've figured that out, I clean things up.

I've seen many junior devs get so worried about the quality of their code, and how they should do things, and omgosh, DRY that they can often become paralyzed and don't just start writing code. I've been mentoring someone for nearly 18 months, and I'm always trying to push him to just start coding and get something working, then come back and discuss and evaluate his work together.

I think you've misunderstood what James has said, and feel compelled to push back on any suggestion that his advice regarding DRY and duplication is borne of any misunderstanding or lack of recognition of the value of DRY. Nor is he someone who I've ever seen stop learning. I keep up with his work, and I'm always impressed by the different things he picks up just because something about it interests him.