Every particle has its antiparticle. It's a nifty, perfectly symmetrical little universe that adds up to a big zero. It's those tiny departures from perfect symmetry, those slight imbalances and oddball imperfections. The big problem for scientists is trying to explain how the primordial perfection shattered ever so slightly to form the universe we call home today. In the beginning was the void, or so Genesis tells us.
Nothing is harder to accept than nothing.
People hate silences, gaps, zeros. So there was certainly a psychological barrier to accepting the concreteness of nothing. Of course, now that physicists have measured the energy of the vacuum and felt the warping of space-time, denying the reality of the void becomes more difficult. It was absurd on the face of it. And that was before people started doing arithmetic with zero and found that it can literally blow number systems apart.