What does the quote Great minds have purposes others have wishes mean?

To me it sounds like great minds set out to do what others spend a lifetime wishing they could do. Some people use their waking hours perhaps dreaming of writing a novel; another person will just sit down and do. We may also see in this saying that whereas many people pass their time satisfying materials needs (eating, sleeping and fulfilling other wishes and desires), to great minds these things are secondary; their main concerns are carrying out some great plans for changing the world.