It sounds like you are describing intuition. I think there are occasional savants born with this, but for the majority of experts that subconscious decision mechanism is honed after years and years of work.
Often it's the other way around. The solution is found, and it is justified with a rationale. But the rationale came later, it is built with knowledge of critical theory and analysis of solutions.
The trouble is you can't teach the intuition.
Just ask them why they pick that certain color and you won't find rational behind it. They just...did, their hand just move to that color, paint it, and it looks good—the results of tons of practices over the years. Not to mention some artist didn't even have proper art education, not to mention art theory. Why and how it happened to be the same combination as in the color harmony theory is surely hard to explain.