Why bitcoin fails: Illiquidity
But bitcoins are not so liquid. Mostly, to buy things, I need to trade them for dollars or another currency. And that is the fatal weakness of bitcoins: at some point, to compete with dollars, it needs to enter the real economy. And if bitcoins become a good way to avoid government surveillance of your financial transactions, then governments will find a way to choke off those entry points so that bitcoins become very illiquid indeed. You cannot have a valuable currency that is good only for the purchase of child pornography and other highly illegal, entirely digital goods.