Why would people ever spend Bitcoin if its value is always expected to go up?

It seems that the general consensus on this subreddit is that BTC will continue to appreciate in value over time.

But in this case, why would people ever spend Bitcoin? Wouldn't it be considered a bad financial decision to do so?

For example, if Bitcoin was the primary currency for a nation, why would it ever make sense for a citizen of that nation to spend Bitcoin if in the long term, its value is expected to go up?

Or is it thought that in a world where cryptocurrencys such as Bitcoin are the primary currency, that they would stop being so volatile and would become relatively stable?