Blockchain in a nutshell adverts to an idea of distributing same ledgers to numerous people in a way that any attacks to
the ledgers will fail because it is physically impossible to hack all the ledgers at the same time. If one ledger is hacked
but the one is not equivalent to the others, the hacking attack will be noticed and denied. This is the strength of
blockchain system.
In other words, the strongness of security system increases when more distributed ledgers are. Here comes a curiosity
that who is going to maintain the distributed ledger and who is going to verify which transaction is right or wrong?
That's why we need a coin system.
There are three systems to issue coins on blockchain system. Here, we only focus on POW system.
POW, proof of power, is the representative of these three things. In order to operate blockchain system, especially here
for public blockchain one, the principle underlying blockchain system is an expectation that honest participants will
sustain the system as long as the existence of the system is going to be helpful for the people engaged. However, no one
will devote themselves for the sake of the system unless there is no reward because maintaining the system incurs
expenses.
For POW which is widely adopted by many cryptocurrencies, the way of making a block and proving whether
transactions are okay or not is called mining. Through the process, verified transactions are going to be recorded in a
new block which will glue to the previous blockchain. This method is so complex that it requires a lot of electricity,
which means that the process itself is to make a cost. That jobs are taken by network participants who are usually called
"Minors".
Here comes a coin system. The myriad of minors can approve a transaction and make a block which leads to reinforcing
the security system of Blockchain. As a reward for this fiddly job, Coins are distributed depending on how much
contributions are made.
That's the reason why we can't detach the concept of coins from "Public" blockchain system.