It doesn't even have to be something during the anime, could be something you thought of later. This happened to me with Erased when I realized I was thinking about it when I was half asleep. http://ift.tt/1VHPTLb
I always thought that Mirai Nikki was gonna be some creepy gorey awesome shit with a great yandere, but no, the end had to punch me straight in the feels, especially the last few seconds... http://ift.tt/1O1YHGn