I live in Europe, and more than a decade ago our national currency was replaced by the Euro. For a few years, everyone calculated back the price in Euro to the old currency when buying something, because it was hard to get a 'feeling' of the price. You can say that once Bitcoin matures, people will also get that feel for it, and don't need the calculate back to USD anymore when shopping, but I have a question about that.
A loaf of bread costs about 1 EUR, and that price has been pretty stable for years. I guess inflation ensures that it will so slowly increase in price, that people get time to adapt. If a loaf of bread costs 0.1 BTC today, it can be doubled or halved in a year, because the speculation causes so much volatility. So I won't develop a real feeling how many loaves of breads I can buy with that anytime soon. And by the time it's widely adopted (and should be stable), all 21M coins will be mined, so deflation will cause the price of bread to fall so much faster than it will rise using an inflationary fiat like EUR/USD.
So how does one develop a phsychological feeling for what 1 BTC is worth?