It seems as though it would be obvious that flaws/imperfections in a diamond would affect the way light is reflected through and from the stone. However, most of what I read says that the cut characteristics are the most important when it comes to brilliance, fire, and scintilation. That being said, how much are characteristics like brilliance, fire, and scintilation affected by the flaws of say... an SI1 stone versus a VVS2 stone for example?