My first personal turning point in my MBA is the following instance:
Sometime in october last year, when our group was solving a case of accounting, we had two issues in a case for which there were arguments. I had a different opinion on both the issues compared to another groupmate who had an opposite view on both. We argued for long and both of us convinced the other on one issue. So he won one and I won one. The next day, when we went to class, we discovered that both of us had convinced each other on the wrong answers. What a fool we had made of ourselves.
This one instance made me realise that nobody can be right all the time and since then, I try listening to other people's ideas without prejuducing their options if they dont match mine.
A true MBA learning lesson.