Hi Ashveen

Here the motive is to show that how much you can learn from your mistakes. Don't give them a piece of an incident that turned out to be not just a disappointment but a disaster. Use a mild incident.

Here's an interesting piece to tell you why!

A person decided to be honest and told interviewers about his greatest mistake. He once sacked someone but got some of the procedures wrong. The employee took them to law and it cost the company 50,000 pounds. He of course did not get the job!!

Here you may admit the mistake if done in the past in the professional job but also inform the interviewer how successfully you have benefited the organisation with your quality of services.

Hi Ashveen,

There is no major or minor disappointment in life, disappointment is actually a learning opportunity that you can use to showcase what has been your takeaway from the situation you were in and How have you improved from the entire experience as a human being when you faced such an obstacle.   

It can be not giving enough time to studies or family or not choosing the subject of your interest or not starting the thing you loved the most earlier in your life.

The interviewer doesn't want to hear your confession he wants you to rather address the situation in a positive outlook, that would encourage hi to hire you for te position you are being interviewed.

 Your answer should reflect your learning and your behavioral change that you have personally witnessed, it can be an emotion of regret or emotion of integrity and empowerment that you choose to highlight. from the situation you were in that you might tag as the disappointment. Everyone has insecurity, confusion, anxiety and other human emotions the idea is how would you handle the same situation when you are on the job/assignment/project once recruited by the hiring manager would you take ownership of the task at hand with success or failure whatever might be the output or would you blame others or give excuse or reason to defend in case of failure. 

That you want to express as a form of your learning from the situation you were in that you might tag as the disappointment. Everyone has insecurity, confusion, anxiety and other human emotions the idea is how would you handle the same situation when you are on the job/assignment/project once recruited by the hiring manager in future. Would you take ownership of the task at hand with success or failure whatever might be the output or would you blame others or give excuse or reason to defend in case of failure?

Remember perception is reality, your story/incident/disappointment that you share as experience/learning should be in such a manner that you are able to highlight yourself as a better and professional candidate.

Take time to wisely decide which incident you want to share and showcase to the interviewer at the time of the interview, your sharing should be authentic and also leaving a positive lasting impression on the listener.  

You can ask your friends/ family members and your teacher which is that moment where they felt you had changed for good and also ask them why they felt so, what difference would be there in case of non-occurrence of the same event made to you and others. 

Their answers would reflect your personal development which when you become bigger that your problems or disappointment.

Hope you would be able to now take this question and reframe it in your own words. 

wishing you all the best.