Objective "Truth" vs. "Perceived" Reality

We were required to write something like this in my English class as a writing exercise. The question was, has there ever been a time where we were wrong about something, but we didn't know it at first. I thought that this was a funny story, so that's why I decided to post it:

One day, I was arguing with Alex; but then again, we always argue. It was the first day of summer school and we were walking up the stairs to the third floor where our class is held. Alex turned to me and said, "hey, your English 112 class was on this floor!" I replied back that it wasn't and that it was really on the second floor. I got really annoyed with him later on because he kept on repeating it, and I just kept thinking "who would know my schedule better than me".

Right before class the next day, when he got me to show him where my English 112 classroom really was, I realized that it was really on the third floor. I felt really dumb and at the same time freaked out because Alex really does know my schedule better than me.