most memorable moment of learning?

As a teacher, I believe that we often assume that students 'get it'. I always try and go back and remember when I was taking a Ceramic Glazes class in college. I had no prior art class experience when I entered college so while I could produce what the teacher was asking for in the visual art classes, I would not have the knowledge base of the terms and medium. Therefore, I would have to wait, hang back and see what the other students were doing after the assignment was given so that I could understand what the assignment actually meant.
So, when I entered the Ceramic Glazes class, I was very intimidated. I had not had a Chemistry class and, of course, that is what you need to have before you begin working with the dry chemicals.
Always before in school I was able to keep pretty good grades with relatively little effort. I could study the night before and pass tests.
So, to make a long story longer, the day we had our final in the Ceramics class, I had studied really hard the night before and thought that I was prepared. When I sat down and opened the test, I realized that I was not. I could actually feel the blood in my whole body drop to my toes and then flush up to the top of my head. I just knew that I was going to bomb on this test.
I tried my best though and actually earned a B on the test.
My point is, I always try and remember that experience when I work on my assignments for my students. Never assume that the students have the prior knowledge that you think they should have.