Paper money is only limited by earth's supply of trees 
At least digital currency is "backed" by the mining's ever-soaring level of difficulty. This built-in scarcity model prevents deflation of bitcoin value, raises the miners' bar for return on investment, and thereby guarantees a steady climb in price. Each transaction buyer wants to hold for a later price rise, and so on down the line. Not every trader can outwait their own need for their own fiat currency, so naturally there are trades at a loss. Whoever has the most patience and greatest wealth can end up with a large hoard of bitcoins.
At least digital currency is "backed" by the mining's ever-soaring level of difficulty. This built-in scarcity model prevents deflation of bitcoin value, raises the miners' bar for return on investment, and thereby guarantees a steady climb in price. Each transaction buyer wants to hold for a later price rise, and so on down the line. Not every trader can outwait their own need for their own fiat currency, so naturally there are trades at a loss. Whoever has the most patience and greatest wealth can end up with a large hoard of bitcoins.
Mining difficulty in no way backs the value of bitcoin. Mining difficulty is only a result of how many computers are solving the algo that mints coins. Whether bitcoin was worth $1000 or $1, it wouldn't directly affect the difficulty of the mining.
The built-in scarcity does not give it a floor value. If that was true, any altcoin with fewer than 21 million possible coins would have a price point higher than bitcoin. What gives bitcoin value is the collective belief by people holding it or seeking to buy it that it will continue to have value. It's just a confidence game.