What is it that causes a person to obsess so about problem? Why one problem and not another?
IMHO, the second question is more instrumental than we think in having made someone known as a genius. Marie Curie would probably not have achieved her fame if radioactivity were not such a "magical" phenomenon in itself, to this day. At the time, radium was immediately hailed as a miracle cure for all sorts of ailments.. Relativity too, is an example of a notion which surfaced exactly "at the right time", and was consequently misused in the most absurd arguments. On the other hand, the synthesis of ammonia, which was certainly of significance for a larger part of the world population (fertilizer..), is only present in the memory of specialists.