"The single biggest difference I have ever seen (over and over again) between a good programmer and a great programmer is how they respond under pressure."

As many have pointed out already, there's a big difference between the pressure of an interview where you've got a couple of minutes to either win the job or completely blow it and a deadline where you usually have several days to plan and prepare.

I would also point out that if management is constantly springing short, do-or-die deadlines on workers then there's something very wrong with their planning.