A person is a maestro when he or she has reached the highest level of competence in a field. The person will be the light for other people, to show direction, guidance, examples, and inspiration to those who follow their path. They do not owe their greatness to praises, nor to circumstance that allow them a spotlight, nor to engineered condition and manipulation, but because they are indeed grand. 

We cannot measure the grandeur of a maestro with numbers. We cannot measure it in sums. We instead assess it from the influence, impact, benefit, of their presence to the environment and to those who have been touched by them directly or indirectly. 

The effects of their presence create change, progress, and even a reversal or deviation from present values to reach a higher place. The greatness of a maestro creates new values and harmony.