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Fiat, gold and bitcoin are means of payment -
but each has its own market. In traditional economic life – fiat is king, gold is a commodity, while bitcoin is the alternative. You can use fiat anywhere - you can also sell gold or use it as a means of payment anywhere, but in some countries you are prohibited from using bitcoin as a legal tender.
The demand for bitcoin will continue to increase over time - it will become more popular among the public year by year. Adoption can be expected to be the best fundamental for hoping for a better future - but of course adaptation to its use cases still has to be patiently expected. Prices will always fluctuate - that is an inherent thing.
"...but each has its own market..."
That's by far the best answer I read in this thread. If someone is a Bitcoin whale and wants to pay a car or a house with Bitcoin where fees are insignificant, that someone might say that Bitcoin was the best money for that specific situation.
If someone wants to pay for a coffee and incurs $20 transaction fees on that day, surely Bitcoin is not the best money for that specific use case.
If someone wants to take cash with them on vacation, Gold is trash, cash can be trash if it is too much as the hassle at the airport is huge, and Bitcoin is simply invisible and essentially limitless in amounts. I often like to say that when it comes to mobility, Bitcoin is the best ever. You can take any amount with you without having to go through any hassle and chances are high you are able to convert it in many countries. I am not fully aware about the current distribution of Bitcoin ATMs globally, but for me it already worked out very well a couple of times.
As you said: each has its own market and it is very use case dependent.