My daughter when she was around 6 years old loved to put on princess dresses and dance around singing. In her mind she looked and sounded like the cartoon characters in the movies.
One day, I pulled out an old VHS camera and set it up on a tripod for her. She danced in front of it for half an hour, recording a bunch of songs. Then she sat down to watch it. After the first few minutes, she turned to me with tears running from her eyes and yelled, "I stink!" She was inexperienced at dancing and singing, but she knew immediately from watching herself that she wasn't very skilled.