It's common for a solution to work perfectly on your local machine but fail on an online judge due to differences in environments. The most common reasons include unhandled edge cases, differences in precision when using floating-point numbers, or slower I/O methods. Online judges have stricter time limits, so using fast input/output methods is essential. Additionally, test your solution with large and small test cases to ensure robustness. Floating-point precision issues can arise due to different system architectures or compilers, so always handle floating-point numbers carefully. Debugging for different environments and ensuring your solution is comprehensive helps avoid these issues.