21 million coins, and most of them are saved, so about 2 million coins out there, if there is 2 million people willing to buy 1 coin per person, and each of them spend $100, the exchange rate will be backed above $100
There are about 200K users maybe, so now each person should be willing to buy 10 coin with $1000 to keep the exchange rate above $100
I like this. The numbers could be off, but the basic idea is that the value of bitcoin is the reservation demand from the users. This is the right way to think.