You are applying to Harvard Business School. We can see your resume, school transcripts, extra-curricular activities, awards, post-MBA career goals, test scores and what your recommenders have to say about you. What else would you like us to know as we consider your candidacy? (No word limit)
The most powerful examples are one where the mistake is personal and the learning is powerful and lasting (e.g. something that has taught you to change the way you work). Focus both on mistake and learning, they should go hand in hand. E.g. On an assignment in a foreign country as a team leader, I did not spend time learning the local culture and the personality of my team members. This created a dysfunctional team environment which ultimately led to delay in the project. This taught me an important lesson to invest time upfront to understand my team mates.
It would be good if your example ties into a story that you have touched upon in your previous essays (e.g. professional or personal). Also, your choice of place and why would convey an aspect of your personality, so think carefully before choosing your example.
4. What is your career vision and why is this choice meaningful to you? Please limit your response to two, double-spaced, typed pages.
Be ambitious in your career vision. Just saying that you want to work in a strategy consulting firm is not ambitious enough (that is easy if you get into Harvard). Harvard looks for people who have the vision to make a big impact in the world. So, be ambitious and bold, yet realistic in your career vision (e.g. entrepreneurship).