What is a monetary good/item?
A monetary item is an asset or liability carrying a value in dollars (or any other fiat currencies) that will NOT change in the future. If I borrowed $1,000 & bought a piece of furniture, I still need to return $1,000 in the future even though that piece of furniture appreciate in USD (USD losing purchasing power).
A piece of paper with printed "$10" on it has a monetary value of $10 now & in the future. Similarly, a Bitcoin address with 1 bitcoin in it has supposedly a "monetary value" of 1 bitcoin (regardless of its USD value) now & in the future.
In comparison to USD, however, Bitcoin may be easily considered as a "non-monetary good" which can rise or fall in value (i.e. USD).
The ONLY way that Bitcoin can become a monetary item (monetary utility) so that "cheap" or "expensive" becomes meaningless in reference to it is by MORE ADOPTION.
Also, the BEST way to kill Bitcoin utility of money/currency is to make it more difficult to use such as high transaction fees, unfriendly interfaces, shutting down, BTCUSD exchanges, etc.
The rise of prices in December could have very well been continued, however, due to ridiculously high fees, IMO, it crashed down in half (& continues for now)!
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For future viewers: price of bitcoin at the moment of posting is 7916.00USD