Reality
Surely reality is a construction - it is dependent of our perception, and might be overthrown by a mere turning of our head. There surely is a truth behind truths, but even if we would be able to sonehow see a reality that is identical to the core reality, how could we ever be sure about it being not merely another fictious world projected through the lenses of our perception? We are entrapped in the existence that is invoked by our own being. Our views, our perception and the reality that results from them is our cage - a cage that defines us, but is, at the same time, defined by ourself. For us, there is no reality outside of it. Within this cage, our beliefs are facts - solid parts of our unique reality. Is every morale a fiction, then? It would be shorthanded to deny the existence if a free will because this cage exists. If we believe in a morale, it becomes a part of our reality, and it is legitimate to apply it to others. By filling the abyss with our ideals, we are able to overcome it.