[Hawking Radiation](https://en.wikipedia.org/wiki/Hawking_radiation) is a is radiation that is predicted to be produced by black holes. Anti-particle- and particle-pairs spontaneously appear close to the event horizon of the black hole. If the anti-particle falls into the black hole, while the corresponding particle can escape, a particle inside the black hole will be annihilated an “radiated away” by the escaping particle.
My question is: why is it only the anti-particle that falls into the black hole? Shouldn’t the particle have an equal probability of falling into the black hole, keeping the whole system at an equilibrium?