Before the Fall, Adam and Eve were in a state of innocence, meaning they knew neither joy nor pain. Though the lack of joy is undesirable, the blessing of ignorance is good: no pain. Because of the Fall, we, like the Savior Himself, gain knowledge one step at a time. Our ignorance methodically melts away.
We might wonder why full knowledge isn't immediately given to everyone. We have to remember that "He who sins against the greater light shall receive the greater condemnation." We are required to live by the knowledge we've been given, and the consequences are greater the more we know. Thankfully, we aren't crushed by more knowledge than we can handle. Instead we learn little by little, so we can grow with the knowledge we receive.