Dream and Vision

I often wonder what is the between "Dream" and "Vision". Do we dream and if those are successful, they are called vision? Or is it a structured dream thinking? Did visionaries know that they would reach desired destination or they are like Columbus the sailor who set with "Strong Desire" to find an alternate route to India and finally landed in New Land, now called USA?
Did Narayan Murthy know that he would create Infosys a multi billion software giant or he set out to fulfil a dream and reached where he is today?
I think it all starts with a dream that looks difficult to achieve. World in general often does not believe that the Dreamer will achieve his dream. Some don't believe the dream but still team up with the dreamer. Then the team prepares the sails to set out. Faith in leadership keeps them hopeful that dream may be achieved. Their faith puts enormous pressure on the dreamer to somehow perform. He/She starts structuring a journey to achieve dream. The Dream converts itself to a passionate story of approach to achievements. Steps start emerging. Risks stare in face. Options start reducing to a create a narrow focus. The focus in turn brings clarity of thoughts. It creates ways to mitigate impending risks and dangers. The dreamer appears to have distinct idea how to reach destination. This is the first time, someone start calling his Dream a "Vision". Success ultimately makes him a visionary!