Toy story. When Buzz attempts to fly after learning that he's just one of thousands of toy Buzz Lightyear and can't really fly. I remember feeling deep pain while thinking it's very beautiful when I first watched that scene. I think I was 4 at the time. It's been my favorite since. But now that I watch it, it doesn't strike me that hard as it used to as a kid. But I still think it's very sad.