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.