Philosophically speaking...
Just because you know something this does not mean that it is there and it is the truth. And just bcoz you don't know, it does not mean that it is not the truth. And since you know both the things ,you  cannot be certain as to what is known and what is unknown. Knowing this paradox will invariably prove that actually and absolutely it cannot be known and hence the unknown will remain unknown & by the same logic known will also remain unknown