Why ACID matters in databases (and why it's not just chemistry class) You know that moment when you transfer money online and your bank app crashes mid-transaction? Without ACID properties, you might lose $500 and the recipient gets nothing. Fun times. ACID isn't just a chemistry term - it's what keeps your data from turning into a mess: Atomicity: All or nothing. Bank transfer either completes fully or gets rolled back completely. Consistency: Data follows the rules. No negative ages or double-booked flights. Isolation: Multiple users can't interfere with each other's transactions. Durability: Once it's done, it's permanently saved even if the server crashes. Real talk: PostgreSQL is ACID-compliant by default. Some NoSQL databases traded ACID for speed but many are adding it back because data integrity matters. Your blog comments don't need ACID. Your payment system absolutely does. Choose wisely, because explaining to customers why their money disappeared is way harder than implementing proper transactions. The chemistry joke writes itself, but the data protection is serious business.