system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why didn't any of the APOLLO astronauts go to the moon twice? Would a crew not benefit by having a member who had already accomplished a very similar mission, in a real environment with all of the associated problems?
gpt
Jim Lovell, David Scott, and Eugene Cernan (e: and John Young, oops) all went to the moon twice though none of them landed on it more than once. If Apollo 20 had happened, Pete Conrad would have potentially been the first person to land on the moon twice.

I think a big part of why NASA ended up doing things this way rather than just sending the same people more than once was that they wanted a good sized pool of the very best people available, and promising them a decent shot at going to the moon was the way to get that.