MongoDB's atomic operators solve single-document race conditions, but multi-document operations across collections like wallets, products, and orders require ACID transactions to prevent partial failures. Using Laravel's DB::transaction() with MongoDB, you can wrap checkout operations so all three collection updates either commit together or roll back entirely. The tutorial covers implementing the transaction, writing tests for rollback scenarios, handling transient vs. business errors with exponential backoff retry logic, keeping transactions fast by excluding external API calls, and creating indexes to optimize performance. Key guidance includes when not to use transactions (single-document ops, analytics, logs) and a real-world hotel booking example.