$0.  First off bitcoin is easily replaceable.  But the biggest reason IMO it will fail is the volatility of the currency.  

Consider this.  

What would happen if someone wanted to purchase a car and had the bitcoin to do so, but the market is a bear market and there's a 20% decrease in the value of bitcoin overnight? What's he going to do?  He had $20,000 in bitcoins one day but the next day he had $16,000 in bitcoins due to the drop.  HODL for a month and wait until his bitcoins are back to being worth $20,000 so he can buy his car?  But the guy needs the car NOW.  He's got a new job and kids and there's no way he can get by without wheels.  

Everybody on this forum just screams HODL all the time and doesn't realize that HODLING through the drops is not going to work out too well for someone who is 100% bitcoin and uses that bitcoin to pay for their food, rent and other bills.