Alan Moore explains
Is it helpful to observe that subjectivity is the only thing that we know is objectively real, or does that just muddy the waters even further, as with so many of the well-intentioned things I say? I mean, we do not experience the universe directly: we experience it only through our limited senses, with our sensory impressions arranged moment by moment into this immersive psychic movie that we agree to call reality. From this point of view, our entire universe can only ever be a subjective neurological phenomenon, at least to us, and a quick glance around will confirm that it’s only us who seem to be much bothered either way about this ontology business. I think Nagel is correct in his criticism of the materialist worldview, and I would further state that even should science ever accomplish its goal of unifying classical and quantum physics, of achieving a grand ‘Theory of Everything’, then if it only describes the physical universe and does not take account of the marvelous, supernatural phenomenon – consciousness – that has arrived at this theory, it is nowhere near a theory of everything, is it? It’s more a theory of everything we perceive, which by definition does not include our own act of perception.
Dasein is an entity bothered about this ontology business.