What is the continuous balancing act defining a star's entire existence while on the main sequence?

Answer

Hydrostatic equilibrium

Hydrostatic equilibrium is the state where the colossal inward crushing force of gravity is perfectly matched by the enormous outward thermal and radiation pressure generated by nuclear fusion.

What is the continuous balancing act defining a star's entire existence while on the main sequence?
heatenergynuclear fusionstarastrophysics