Actually, a space vehicle doesn't have to work perfectly. Apollo 7 (the 'back to space' mission following the Apollo 1 pad fire) was hailed as one of the most productive development missions of the Apollo program - yet there were over 500 failures, some of them mission-critical (like an annoying tendency for the nav computer to crash at inopportune times) in the eleven days of the flight.
Perfection isn't required - but failures need to be capable of being recognized and either corrected or avoided before 'mission-critical' turns into 'mission-ending.'
I agree, however, that NASA is not a rental-car company. Space travel, as far as I can see, is always going to be an inherently dangerous activity. Every pilot is a test pilot, and despite the rhetoric, there is no such thing as a routine mission.
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