I see what you're saying now. You're basically describing deflation. Yeah people would buy bread (and other essentials to live) but as their currency would be more valuable tomorrow they'd put off buying non essentials. In fiat currency this is seen as prices dropping in bitcoin is seen as the value of the bitcoin going up.

Why would I buy a non essential today when I know it'll be 10% cheaper tomorrow?

Why would I use my bitcoin to buy anything non essential when if I wait until the next spike it'll be 30% more valuable than today?

The answer of course is I wouldn't. I'll buy it later when it's 10% cheaper for my fiat currency or 30% cheaper if I'm using bitcoin. It's not an essential so why spend more to get he same thing.

Currency needs stability in fiat currency to much instability is described in terms of inflation and deflation. Because bitcoin is more of an investment than a currency it's described as it going up and down.

As there's no intrinsic value to bitcoin and because there's no central backing working to maintain the stability it'll never be anything other than a speculative investment for people who're already rich or the few who get lucky to make some actual useable money off.