What are the most important concepts in Back End Development?

Following are some of the most important concepts a Back End Developer must know:
• Performance of the Web/Mobile backend service is one of the most important concepts but is only looked at when the problem arises.
• Logging and Error Handling - Any error that occurs in production must be logged with all relevant facts, and the developer should have included the log messages from the start so that he can quickly trace the problem back.
• Security is another important concept that should provide authorization by choice and not by default.
• Load Balancing is a concept that should be mastered in order to prevent fallout effects from the same.
• Session Handling and its Effects on Performance, Scalability, and Test Automation.
• Database design - there will always be one excellent backend engineer on every team who can advise the DBA whether the database design is good or poor for the problem they are trying to solve. The developer will be able to make more efficient calls to the database if they are familiar with queries and tables.