One of the mysteries of our world is why there is any matter around at all. Every particle has an antiparticle that has the same mass as the particle but with opposite charge and quantum spin, and antiparticles combine together to form antimatter as ordinary particles combine to form matter. Both particles and antiparticles are equally affected by gravity as gravity depends on mass.
Mixing particles and antiparticles or matter and antimatter together can lead to the annihilation. One particularly famous case of fine tuning involves the production of carbon and oxygen in the stars through nuclear reactions that requires a delicately arranged process where hydrogen burns to form helium, which then ignites to form carbon and oxygen. The energy levels for these two are just right for life and famous astronomer Fred Hoyle.
Hawking has noted that the difference in the mass of the neutron and the mass of the proton must be approximately equal to twice the mass of the electron, which is the case. Earth is just the right size to support the right kind of atmosphere and atmosphere thickness that we need. If it was smaller like Mercury, it couldn’t support an atmosphere, while if larger like Jupiter it would have a poisonous atmosphere of hydrogen.