Inflation can exist because of a lot of things: natural loss of value, resource scarcity, monetary policy, greed, etc. And it's even harder to make sense of with fiat currency.

> Seemed like a vicious cycle.

The issue is inflation and deflation both tend to be positive feedback loops. Inflation can promote behavior that promotes inflation. Deflation can promote behavior that promotes deflation.

Note that I use "tend to" and "can promote". It's all based of off assumptions on how people value things and their behaviors, as is all economic models.

> why prices HAVE to keep going up

It really doesn't have to. We do so because economic models show that we should because of the way we behave. But, we also behave the way we do because of the economic systems that we've designed.

Prices have to keep going up if you want a system that promotes endless consumption and growth in consumption.

It also lets you have a "non-zero-sum" economy, where it appears everyone is making a "profit". But, in reality it isn't.