What Keeps Keeps the Fire in your Bones?

I have always like the phrase, "Fire in your bones." For whatever reason it conjures up images of my ancestral blacksmiths foraging bones of iron for their progeny. So what is it that keeps you going? What keeps the forge hot? So hot that it can manipulate the iron of your experiences and mold it into things that support you instead of dragging you down?
For me it is the "what if." What if I have the potential to do that? What would it feel like to be able to do that? What would my perception be like if that was something that I could do?
If you never try then you'll never know.