We all like to feel like a mentor. This is the person's dream and it will give them a chance to fantasize. You will notice that people will take a few minutes to really ponder their answer. This is an opportunity to do a little bragging. This is a great question.
People love to tell the story of change.
This is a great speculator question, which should provoke insightful comments. This gives people the opportunity to share their war stories. This accentuates the positive. You are not looking for secrets, merely admiring business acumen. People will almost always stop and think before answering this question.