Just an observation, but if you can't hack an interview without chemical assistance, how will you cope with a full-blown emergency at 33,000 ft?
Good question but rather simple to answer.....
It comes from an intense desire to prove they could indeed cope with a real emergency. The nerves come from them hoping to god that this will shine through at interview. With advance warning it's very easy to work oneself up but real life emergencies by their very nature are immediate affairs and you don't get time to become nervous.
I know guys who comes across as nervous characters on the ground...... put them in an intense situation upstairs and they're a different person entirely.
Hope that clears it up for you.
VFE.