The answer has to do with what money is, money in reality, not what the dictionary or governments say it is.
When the price of an item at the store goes up or comes down, the price remains the same
if you consider the item as the money rather than the US Dollar as the money. Consider Bitcoin. The price of a bitcoin in relation to another bitcoin is still the same. If you want to buy a bitcoin with a bitcoin, you will always be paying a bitcoin for the bitcoin you buy. Therefore, it is not the bitcoin price that is fluctuating. The bitcoin price has never fluctuated. It is the price of the US Dollar that is fluctuating. You simply have an incomplete focus.
Why doesn't the dollar fluctuate in price with regard to
all other items the way it has been with Bitcoin lately? It's because of the people and the stores that sell products and items. Actually, there is great variance of prices between stores. Just look at airline prices on the Internet. Look at appliance prices for the exact same product made by the exact same manufacturer. There is great difference in price depending on where you look. Yet, if you want to swap one refrigerator for another that is exactly the same, the "price" is the same also.
The whole point revolves around the kind of value people place on things, and the methods they have available for evaluating value.
People would be wise to become better investors with everything that they buy, by evaluating
all products with the idea that the products are
all different forms of money. Don't look at the dollar as money. Rather, look at gasoline as money when you are at the pumps. Look at food as money when you're at the grocer. Do it so that you start to get the feel for trading rather than placing all your eggs in the US Dollar as money.
When enough people want Bitcoin, dollars will become a thing of the past. Then, after the Internet collapses, we'll be back to barter, or gold and silver.