In my experience, when one has an immediate answer to every problem, that is a sign that one does not understand the problem. Every non-trivial story needs some ugly code to account for a pathological edge case that the "just do X" developer isn't thinking about.
It's a sign of being a know-it-all.
“Just do...” is oversimplification.
If you can explain how to do something that others are finding difficulty in, it’s a. Arrogant and b. Probably not understanding it fully to say “just do X”