Thinkitis sufferers think constantly. Ideas breed more ideas, analysis breeds more analysis. This is not to say that all the thoughts are great thoughts. The sufferer just can't stop.
I believe all the major inventors, philosophers, composers, artists, scientists and other luminous intellectuals have thinkitis. That does not mean every thinkitis sufferer will produce great work. But that makes it all the worse. One can understand the compulsion of genius without being a genius.