Why do we forget our dreams?
One theory of dreaming is that when you wake up, your brain is trying to reconstruct the events you dreamed of, into a logical story that makes sense. If it cannot do it fast enough, you forget the dream.
However, the fact that you forget your dreams does not mean you don't remember your dreams. The memory is there, it's available, it just isn't consciously accessible at the time you want to get it.
Matt's theory is that we retain all our dreams and they subconsciously impact everything we do every day, we just don't know that.