Pretty disappointed on the comments here (this was written when people were saying moon landing was fake)... The training had to be exhaustive, there was no retrying. Each Apollo mission was an important step from the previous. They had to be prepared for just about anything and know how to do each step of the mission in their sleep. This kind of redundancy has always been there in manned spaceflight including the shuttle. One cool thing they have to assist in training these days is virtual reality training. Here is an image: http://www.nasa.gov/mission_pages/station/multimedia/gallery...