A solution passing sample tests but failing on submission is a common issue in competitive programming, often due to unhandled edge cases, input constraints, or precision errors. First, analyze if you've covered all possible edge cases, such as the smallest or largest inputs allowed by the problem constraints. Solutions might fail if they don't handle special scenarios, like empty arrays, single elements, or extreme values. Another common cause is precision error when working with floating-point numbers; using integer math or rounding can often fix this. Additionally, check if you're using the right data types to avoid overflow in languages with strict type limits. Debugging tools and custom test cases can help you trace where the code diverges from expected behavior, ensuring a more robust solution.