"Kowledge: the awareness or familiarity gained by experience of a fact or situation." - http://www.oxforddictionaries.com/definition/knowledge
The moment you hear something you shouldn't have, or realise that what you had just heard or read is something you would rather forget and that it wouldn't benefit your current state of mind in any way... it's too late. Yes, it's too late, the unwanted "knowledge" just corrupted your mind - nothing will ever be the same again. From now on, your "pure" idea of what was, is now a corruption of what is. Pre-supposing now is the field you're an expert in and any further encounters with what you thought something was, will now fully be judged and analysed by your wonderful mind filled with unwanted knowledge. Your view of the world will change. Your idea of the people around you will change. You will change. Unknowingly you will act and react different towards people and ideologies. Change is upon you - suck it up. Never again will you get rid of the Unwanted Knowledge that infiltrated your mind. The world and its people will be much less innoscent in your eyes. Your awareness of any future event or situation will be sharpened and more and more in tune. Unknowingly the unwanted knowledge creeps your brain and pollutes your future.