A recent feature update on the Cardano blockchain caused a "catastrophic" failure that wiped out over two years of transaction history. Thankfully, this occurred on a test net and although no real funds were lost, this Cardano example brings up a good point that applies to the broader cryptocurrency world. What is a test net, how do they work, and why are test nets so important to cryptocurrency blockchains? As always, this is not financial advice. Rather it is my best effort attempt to provide general cryptocurrency education.