Take the bitcoin blockchain for example.   The transactions that go into bitcoin cannot exceed more than a million-bytes every ten minutes.  The amount of transactions that are issued by bitcoin users has exceeded this value.   If you want to send money and I want to send money using the bitcoin blockchain but there is only room for one more transaction, how do we decide who gets their transaction into the block?

Bitcoin solves this with transaction fees.   Who ever pays the higher transaction fee gets to send the transaction.  Steem solves this by rationing the number of transactions a person can put in the blockchain per unit of time based on how much Steem power each one has.   If you have double my steem power, you can send twice the amount of transactions per unit of time than I can.