I have just watched this fantastic recent video about how Bitcoin and other blockchain-based cryptocurrencies actually work. The clarity of the explanation is incredible!!! Very highly recommended.
Kudos to the author 3Blue1Brown!
One thing that worries me personally is that as the rewards for mining decrease, the mining difficulty increases, the miners are forced to keep increasing the transaction fees to cover the huge mining costs. Mining Bitcoin has become so capital intensive that one guy even wants to have a hydroelectic dam to produce electricity to power his huge mining rigs.
What if the miners decide it's not worth it and move to some other currency? No transactions will go through the blockchain or it will take huge amount of time (or even never)....