Fundamentally, I believe, the main issue is that we have a tendency to believe or think that "reality" (the world/universe), is separate from us. But we cannot separate our perception or experience of reality from it. If I don't exist, then _my_ reality doesn't exist. And there's no way for anyone to experience anyone else's reality. So all individual realities are that, individual, and maybe a lot of us can agree on some stuff, but that doesn't necessarily mean that stuff is objectively real for everyone/the universe. We each individually assign meaning to our own experiences and then need to deal with the (maybe apparent) difference in meaning or interpretation among ourselves.

I believe the next big revolution in physics is going to come from incorporating perception and "the observer" as a fundamental part of the models. Consciousness, from my perspective, is the only way we have to "know" the world, which to me means that consciousness is even more basic/fundamental than matter, time or space. And so far, the whole field of physics has been pretty much ignoring it ️