Why gold and bitcoin make lousy money: A desirable property of a monetary instrument is that it holds its value over short periods of time. Most assets do not have this property: their purchasing power fluctuates greatly at very high frequency. Imagine having gone to work for gold a few weeks ago, only to see the purchasing power of your wages drop by 10% in one day. Imagine having purchased something using Bitcoin, only to watch the purchasing power of your spent Bitcoin rise by 100% the next day. It would be frustrating.
Is it important for a monetary instrument to hold its value over long periods of time? I used to think so. But now I'm not so sure. While I do not necessarily like the idea of inflation eating away at the value of fiat money, I don't think that a low and stable inflation rate is such a big deal. Money is not meant to be a long-term store of value, after all. Once you receive your wages, you are free to purchase gold, bitcoin, or any other asset you wish. (Inflation does hurt those on fixed nominal payments, but the remedy for that is simply to index those payments to inflation. No big deal.)
I find it interesting to compare the huge price movements in gold and Bitcoin recently, especially since the physical properties of the two objects are so different. That is, gold is a solid metal, while Bitcoin is just an abstract accounting unit (like fiat money).
But despite these physical differences, the two objects do share two important characteristics:
 They are (or are perceived to be) in relatively fixed supply; and
 The demand for these objects can fluctuate violently.
The implication of  and  is that the purchasing power (or price) of these objects can fluctuate violently and at high frequency. Given , the property , which is the property that gold standard advocates like to emphasize, results in price-level instability. In principle, these wild fluctuations in purchasing power can be mitigated by having an "elastic" money supply, managed by some (private or public) monetary institution. This latter belief is what underlies the establishment of a central bank managing a fiat money system (though there are other ways to achieve the same result). ...
The key issue for any monetary system is credibility of the agencies responsible for managing the economy's money supply in a socially responsible manner. A popular design in many countries is a politically independent central bank, mandated to achieve some measure of price-level stability. And whatever faults one might ascribe to the U.S. Federal Reserve Bank,... since the early 1980s, the Fed has at least managed to keep inflation relatively low and relatively stable.