An atom has a nucleus which is positively charged due to it's one or more protons. Around the nucleus swarms one or more negatively charged electrons. The atom as a whole is neutral, the positive and negative charges balance each other.
Now, we know from simple experiments with static electricity that positively charged things get attracted to negatively charged things. We also know that atoms take up space, they have a size. So that raises a question about our atom: How come those negatively charged electrons don't fall in towards the positively charged protons and the whole atom collapse into a single point?
We could speculate that the electrons are orbiting the nucleus and that the centripetal force of the rotation keeps the electrons from falling into the nucleus. Rather like the way the Earth does not fall into the sun as it orbits.
But, we also know, from experiments with electricity and Maxwell's equations that an accelerating charge generates elecro-magnetic waves that radiate into space. Those waves carry away energy. An electron orbiting a nucleus is under a constant acceleration so it would be expected to radiate away it's kinetic energy and the orbit would decay rather quickly until the electron fell into the nucleus.
This does not happen.Why not?
Well because, because the Pauli Exclusion principle.
Thing is, it's a principle. It has no proof. One can only observe that it is so and state that it is always so as a principle. https://en.wikipedia.org/wiki/Pauli_exclusion_principle
Of course there is a lot more to it than I mention above.
Memory in C++ is a leaky abstraction .