* It's incredibly massive: The sun contains an enormous amount of hydrogen, roughly 75% of its mass.

* Nuclear fusion: The sun's energy comes from nuclear fusion, where hydrogen atoms are converted into helium, releasing tremendous amounts of energy. This process is incredibly slow, converting only a tiny fraction of its hydrogen into helium each second.

* Slow burning: The sun's core temperature and pressure are just right to sustain a slow and steady fusion rate. This ensures that the hydrogen fuel is consumed over a very long time.

* Hydrogen is constantly replenished: While some hydrogen is consumed in fusion, the sun is constantly pulling in more hydrogen from its surrounding nebula, replenishing its fuel supply.

However, the sun's hydrogen will eventually run out:

* Hydrogen depletion: Over billions of years, the sun will eventually deplete most of its hydrogen fuel.

* Expansion and cooling: As the sun runs out of hydrogen, it will expand and cool, becoming a red giant.

* Helium burning: The sun will then start fusing helium into heavier elements, but this process will be much shorter and more intense.

* Final stage: Eventually, the sun will run out of all fuel and collapse into a white dwarf, a dense and faint remnant of its former self.

In summary, the sun doesn't run out of hydrogen because it has a vast amount of it, consumes it slowly through nuclear fusion, and constantly replenishes its supply. However, this process will eventually reach its end, leading to the sun's evolution into a red giant and then a white dwarf.