 Why is Si retirement so significant to the Space Exploration Team?
What's more important—Man's conquest of space, or one spaceman's life? They also had a banquet for him, complete with speeches by such bigwigs of the Department of Space Exploration as Academician Lofting Gubelin and Doctor Hans Girard-Perregaux. It was better to retire on a limited crediting, on a confoundedly limited crediting, than to take the two or three more trips in hopes of attaining a higher standard. He'd had plenty of time to figure it out, there alone in space on the Moon run, there on the Venus or Mars runs. Automation being what it is, only a fraction of the population is ever called up. His industrial aptitude dossier revealed him a possible candidate for space pilot, and it was you yourself who talked him into taking the training ... pointing out the more pragmatic advantages such as complete retirement after but six trips, added shares of Basic so that he could enjoy a more comfortable life than most and the fame that would accrue to him as one of the very few who still participate in travel to the planets. He is now legally eligible for retirement. He was drafted into the working force reserves, served his time, and is now free from toil for the balance of his life. The man is the only trained space pilot in the world.
 Training new spacemen is costly and time consuming. They won’t have anyone else ready after him.
 There aren’t enough working people in the world. They won’t be able to find a replacement.  As one of two remaining spacemen, it would likely mean the defunding and shut down of the Space Exploration Team.  Training new spacemen is costly and time consuming. They won’t have anyone else ready after him.  His retirement may inspire others to stop working as well, which would be hugely detrimental as most people don't feel the drive to work as is.