I was talking to my brother yesterday evening about some of his lecturers who grade based on comprehension over the text, not about what the students can do with what they've learned. Then we talked about how several lecturers, mine included, who refuse to be corrected, challenged, and questioned in class. They would be defensive and even flunk the student out of spite.
As a lecturer and researcher, going on my seventh year now, I have experienced being imprecise in class. It was in those first years that I felt the surge of insecurity, thinking about the possibility that after admitting not knowing, students would question my credibility altogether.
But this risk is always, always undermined by the fact that the best ways to learn is to admit not knowing. After lectures, I learn more than I knew before, because students are willing to contribute what they know into the framework that I've introduced. The classroom becomes an interaction, a dynamic, instead of a linear process of knowledge transfer (and what is knowledge, anyway, if not continually challenged).
And afterwards, seeing hands rising at the end of a lecture becomes gratifying. That those textbook science goes beyond the classroom, to everyday life, to how we handle personal and social trials. That a thought could generate a string of questions, furthermore shining light on other issues and finding answers is why I think human beings began thinking in the first place.
We should all consider ourselves students, because the best of mentality is one that allows mistake - and learns from them. It's how we better ourselves, develop our potentials and come out sharper.
After all, the moment we think we know it all is the moment we stop learning - which makes it the moment we're officially ignorant.