The question is, what is a great mind? Often, the more you think about a saying, the less it makes sense. Its all relative. What are you referring to as being great?(rhetorical question) Is it the fact that someone can imagine anything, as though they're actually seeing it? A person who can glance at something, then draw it perfectly, weeks later? If they can do trig in their head, in seconds, does that mean they have a great mind? In my opinion, we all have great minds, in very different ways. I can add long chains of numbers in my head, draw a picture as I see it, play a song on trumpet twice and remember how to play it forever, and take amazing pictures, yet I suck at creative writing. We all have our strengths & weaknesses. In some convoluted way, they balance out.