Anything from making a mistake on an experiment that would ruin some scientist on earth's experiment - career, potentially - to doing something wrong with the satellite that a country was depending on for its communications, to making some mistake that could actually cost you and the crew either a mission or your lives. So there is a lot of pressure that's put on every astronaut to just make sure that he or she understands exactly what to do, exactly when to do it, and is trained and prepared to carry it out.
Sally RideThe best advice I can give anybody is to try to understand who you are and what you want to do, and don't be afraid to go down that road and do whatever it takes and work as hard as you have to work to achieve that.
Sally RideAfter the Challenger accident, NASA put in a lot of time to improve the safety of the space shuttle to fix the things that had gone wrong.
Sally Ride