Software suffering from Bug!
1. Incomplete, incorrect, inadequate, vague, missing document. In a nutshell, error of requirements.
2. Deficient/defective design.
3. Miss perception of requirements.
4. Miscommunication or no communication.
6. Insufficient knowledge on implemented technology.
7. Programming/coding errors.
8. Logical error not handled effectively.
9. Poor management on team forming and driving to devise product.
10. Project coordination gap between team.
11. Lack of convention knowledge and its implementation.
12. Wrong project estimation and plan; ultimately pressure fall upon whole team.
13. All possible test cases are not covered.
14. Insufficient time to test.
15. In appropriate use of methodologies.
Robustness Achievable If:
1. Requirement must be standard, details and complete with all relevant information.
2. Entails requirement analysis accurately.
3. Submit good questionnaire to understand each point of the specification.
4. Team discussion on each backlog items.
5. Flawless design.
6. Forecast possible complexity (use experience as an example).
7. R&D on coming up complexity.
8. Realistic plan to meet the deadline safely.
9. Must have confident and knowledge to implement backlog items.
10. Basic acceptance test must for module owner.
11. Must raise hand | flag if anybody stuck in any issue.
12. Need to make sure code coverage.
13. Use proven code (if possible).
14. Peer code review (if possible).
15. Detail error report | log for further analysis.
16. All possible test cases must be covered.
17. Make sure all possible performance factors.
18. All possible test scenarios | environments setup before extensive testing.
19. Automate stable portion to reuse it in regression.
20. Have to make sure browser and device compatibility.
21. Have to bug advocacy in a right manner.
22. Have to stop blame game rather focus on project success.
23. Have to keep attention on client feedback.
24. Have to validate deployment to make sure successful build.
25. Good team work! Good team work! Good team work! And finally smile together!
Perhaps I have missed some points...