bitcoin is you can earn through mining with the use of computer processors to mine and it's called blockchain
every blockchain have difficulty, i don't know what is difficulty in blockchain.. and bitcoin is very special... with the use of miner like Sha 256 and antminer s9. and mining software direct to your wallet and you can convert it as currency, the bitcoin is digital currency because you cannot touch it, but you can convert it as money..
another special in bitcoin, is non taxable.. because they not monitor the bitcoin. because bitcoin is decentralized blockchain..