You don't understand - what would you know?

I watch a lot of anime and have had frequent interactions with Asians over the course of my life, and one particular sentiment that is expressed by this ethnic group is "you don't understand!", or "what would you know?" At first I thought this was a normal expression of frustration but the more I consider it the more I think this is wrong.

The reason I'm starting to think I was wrong about this is the fact that it is NEVER followed by a true declaration of intentions, feelings or thoughts. They never deign to express themselves after saying this.

Usually it's a second- or third-string character that says this; it's a weak comeback to a brutally honest accusation. "What would you know about it?" isn't even a denial - it's a fearful response to the blinding face of truth. Only minor characters use this rhetorical question as any main character always knows where they stand - they have no need for such an underwhelming rejoinder. Even the primary antagonists will never say this - they have resolve and (typically) an evil determination. The hero, when faced with a harshness will either proudly declare their belief, or they will be stunned into catharsis.

A teacher, a leader, the determined, the proud - these are all people who never say "you don't understand". In Western culture it tends to be used only by whiny teenagers stricken by angst over adolescence.