A childhood belief about adverts

I used to believe tv commercials were not played from tape, but their actors had to perform live in front of camera every time the commercial was emitted. I remember how I wondered about commercial with group of kindergarten children listening to dentist and answering his question - "man, how poor they are, being such a child they have to play the same scene thousands of times and to do it completly the same each time" It was just one day when I realised, "Hey it is impossible to make perfectly identical moves so many times!" Then I said to myself "Ya fool, what are cassetes for!" =)