That means, people will no longer value things based on Fiat, but rather Bitcoin itself. You would pay for things directly on Bitcoin (for instance 0.000025 BTC for a cup of coffee) without the need to worry about its current exchange rate (or price) relative to Fiat. If that happens, then Bitcoin will "stabilize" effectively proving its use as digital cash.
Hihi, no you won't have problems with the price in USD or your local currency but that would still mean the prices in
BTC will not be stable themselves, and they will never be. If everyone, every single person would ditch fiat and stick to a limited supply of coins depending on the number of goods transacted or the size of the economies on global level prices will still be floating around, so there won't be true stabilization.
If for example we would only had bitcoin during this covid mess prices would still have gone up, it's a matter of supply and demand so although 1 bitcoin would have bought you more goods than the equivalent in USD over a longer period it would still have been less than a year an ago. Same for the other situation where you have an economic boom and it will be more valuable in terms of what you can buy with it.
The 0.000 thingy is a false problem anyhow, switch to satoshis, if poeple can deal with paying 20000 VND for one liter of gas they for sure will have no problem paying 5000 sat for the same.