You try your best but not comprehend a certain topic for a very long time and eventually you begin to understand it. At this point you would feel sad because you spent so much time on trying to understand this very topic and realize that the topic was actually pretty straight forward to comprehend. What's word for this sad emotion you feel at this very moment? Thanks!
Edit: Thank you for the suggestions. Epiphany is close but it does not represent the sadness of the moment.
Edit3: Not catharsis.