Just as in a crowded room each new person sharply increases the pressure on the walls, in a neutron star increasing density leads to a rise in internal resistance. But even this resistance has an absolute ceiling. Physicists describe it with the ratio of pressure to energy density (the quantity φ) — a sort of measure of matter's "stubbornness." From special relativity, φ cannot exceed 1 anyway (otherwise signals inside the star would outpace the speed of light). And general relativity, adding spacetime curvature, tightens the limit even further. The key ingredient is the stability condition: the star's mass must increase from center to edge without gaps. With it, φ does not exceed 0.385. This number works for any conceivable star filling, from ordinary neutrons to quark soup. Surprisingly, the same law applies to water in a glass — it's just realized at negligible fractions of a percent, so we don't feel it.