Is Priori Knowledge Important?

One of the basis of Plato's arguments is that all human beings posses the prior knowledge, the "good" knowledge.  However, as humans we must recall that knowledge as we move on through life.  My discrepancy with this theory is what determines if we have actually recalled or found that "good" knowledge.  How, as human beings, are we supposed to know what knowledge we come across is good or not?

I suppose my point touches on the grand question, what is the difference between right and wrong.  However, I believe Plato's theory proposes too broad of an answer. 

Response to "Another interpretation for Plato's Metaphysics" - Corbin Brassard

"Plato believed that a world of forms existed and that the reason people can see two different, unique objects both as chairs is because they are both attempts to replicate the form of chair. I think it is because humans have the ability to reason and look at the shape of the objects and see that they are most likely to function as chairs... and that its our ability to comprehend the function of the materials that makes it a chair."

The above quote is what struck me most about Brassard's post.  I am in total agreement that Plato did not "capture the full truth" when speaking of his Theory of Forms.  Without humans to determine what a chair is, would there be a chair? If a human did not think of the word 'chair' would there be a chair? Yes, there would be a chair but it would be a completely different concept.  The entire idea of the Theory of Forms makes sense, but like Brassard said, it is incomplete.