It's really just the combination of a hard cap on supply and human greed. If those two things are real and exist, it has to go up.

Why?

The price is a function of supply and demand. We already know that supply is fixed at 21 million.

But what about demand?

The hard cap is actually also responsible for demand, because bitcoin is the only asset in existence with a verifiable hard cap. And as we are seeing, this is something that greedy people value. Because it makes the price always go up when demand goes up. When the price goes up, the demand goes up. It is a self-fulfilling prophecy.

The only caveat is if there is a bug in the code or in the system. Then it could become worthless.