The life of a star is a constant struggle between the thermal pressure of the hot interior pushing outwards, and the gravitational weight of the stellar envelope pushing inwards.
The thermal pressure is maintained by energy input from thermonuclear fusion,
first burning H into He, then He into C, then O, on up to Fe.
As the star approaches the end of its life, thermal pressure loses the 10 million year battle to gravity...
There is yet no working theoretical model that can explain how this death sequence turns into an explosion of 10^51 ergs, but perhaps convection is important?
