Bitcoin Q&A: What is the Appeal of Sound Money?

What functions of money does the current stage of bitcoin fulfill? What is the current popular use case? Why will unit of account be the last function we achieve? Which use cases will accelerate bitcoin adoption in western countries (ex. Germany)? Why should we not be so hard on speculation and hedging against devaluation? What is the appeal of sound money? Will bitcoin become a world reserve currency? Why is gold not a good medium of exchange? How do we incentivise spending of bitcoin, when the current trend is to hold? Why is HODLing simultaneously hard? Why do mainstream economists call it "hoarding" instead of "saving"?