This is actually a very relatable post. I saw many of these things happen when I was in the uni. The whole class will agree not to attend a lecture because the timing was not suitable for all, yet some persons will go ahead and attend that lecture.
This just proves how unreliable humans can be. When we keep this in mind, we are less likely to be disappointed.
Funny enough this happened recently at my school. Fortunately for those of us who were not present, the lecturer decided to postpone the class.
Lol I can imagine how the others must have felt. Good for them