“It works on my machine.”

“It works on my machine.” You’ve probably heard this before. I tested the application. Everything works perfectly. Then I send it to someone else. Suddenly, it doesn’t work. I check the code. Same code. So what changed? The environment. Maybe my machine has: A different Node.js version A different database setup Missing environment variables Different package versions Different operating system settings A dependency that behaves differently on another machine The code may be the same, but the environment running that code isn’t. This is one reason tools like Docker and proper environment configuration are useful. They help make the application run in a more predictable and consistent environment instead of depending on whatever happens to be installed on one developer’s machine. So the next time someone says: “But it works on my machine.” Don’t immediately assume the code is fine. Check the environment too. Because sometimes “it works on my machine” isn’t the end of the conversation. It’s the beginning of the debugging.