I think what this interesting and thought-provoking statement is trying to suggest is that if a situation is "abnormal" or out of the realms of our experience and undestanding, it is therefore "normal" to react "abnormally" to it, because it is so abnormal. This statement uses a double negative to suggest a positive, by stating that two abnormals together create a normal. I suppose it makes sense if you think about it. Let us just take an extreme example. If aliens invaded the planet, this would definitely be an abnormal situation. In response to this, we would expect people to act abnormally, crying, screaming or showing extreme emotion. However, according to this statement, this would be a normal reaction because of the abnormality of the situation. Normal reactions are reserved for normal situations which we understand and can interpret. It is only normal therefore, for an abnormal situation to produce an abnormal reaction, which would cancel out the two abnormals making the response normal. If you get what I mean!