What seperates the World Class from the Very Good?

[Mikey]

I sit here and wonder sometimes wonder what is the determining factor that seperates World Class Players from very good players.

I am sure we can think of many World Class Players off the top of our heads but then there are very very good players.
But the truth I would like to be revealed is what is the determining factor or factors that seperate these two players.

Is it a better understanding of the game at hand or is more of a perfect application of theories and concepts consistently coupled in with the fact of additional skills such as intuition or remarkable memories that seperate the two classes?

I am hoping Barry G. can offer some insight to what distinguishes the two classes.

Thanks in advance.