A personal example can be appropriate if it reinforces your pattern of accomplishments. Talk about results of achieving your goal. This indicates you set realistic goals and that you can focus on outcomes. Select an example that has interesting outcomes related to your efforts. The example should showcase your skills and abilities. Finally, talk about what you have learnt from this process and how you have taken on these lessons in your life. This will show the interviewer that you have reflected and drawn from your experience.