Yes, this happens.

As for how the scientists and engineers feel, the only way to really rationalize it is to take a very utilitarian "the benefits outweigh the harms" approach to the work. In general when you're working on stuff that can kill people that's the approach you have to take: in any complex system like a car or plane there will be some combination of failures that will kill everyone aboard. But you do the best you can to minimize those, and you sleep at night.

It's when you know you could have done more and weren't able to that the inability to sleep at night occurs.

Annie, we cannot guarantee you safe return of John. This would be lying. Nobody can guarantee you this – there is too much machinery involved. The one thing I can guarantee you is that when the spacecraft leaves it is in the best possible condition for a launch. If anything should happen to the spacecraft, I would like to be able to come and tell you about the accident and look you straight in the eye and say, 'We did the best we could.' My conscience then is clear and there is where my guideline is.

- Günter Wendt, Launch Pad Supervisor, Mercury and Gemini programs