Price.

The fiat price is a reflection of the willingness of people to part ways with their fiat to get Bitcoin.

The higher the price is, the more people want Bitcoin in comparison to fiat.

When people start truly losing their faith in their fiat currencies big time, like Weimar Republic grade disrespect, the price will go through the roof.

Eventually we will reach the final station: the price will be infinite. For no one will sell their Bitcoin for any amount of fiat.