The author, Tony Dang, shares the story of Infisical's decision to migrate from MongoDB to PostgreSQL, a database management system. The company had grown rapidly and needed to upgrade its stack to handle increasing usage demands. They chose PostgreSQL due to its ease of management, built-in support for transactions, relational capabilities, and extensive documentation. The migration process was complex, involving the re-write of dozens of data structures and hundreds of queries across the application. Despite initial challenges, the team successfully executed the migration within a six-hour window with minimal downtime, resulting in significant performance gains, improved data validation, and easier self-hosting capabilities for customers. The author concludes that the initiative was highly successful and recommends careful planning and discussion before attempting similar big endeavors.