This is tempting, because we have a tight grip of control theory. However, there are thousands of things you could measure, and picking one at a time to improve

This is tempting, because we have a tight grip of control theory. However, there are thousands of things you could measure, and picking one at a time to improve could be catastrophic. Give a severely depressed person a big bump in motivation and nothing else, and it might be their end. We'll need to pick a collection of probably at least 100 measurements of various personality facets, try different therapies and medicines, and see which ones reduce the average error the most for different starting conditions. And do this consistently. Then, maybe we can say things like "given your scenario, treatment X will improve your overall condition the most but may leave these facets suboptimal, and treatment Y will provide a slightly lower overall improvement but does better for these facets you were most concerned about" with actual mathematical confidence.