you could apply the same argument to most aspects of most sports, or other other stressful situation come to that.

Pressure invites mistakes, but if it's a situation you have practiced and rehearsed often enough, the neural networks involved in carrying out the task will be more firmly established and so a favourable outcome becomes more likely. Of course the nerves have to be brought under control as well for this to succeed. Pressure basically boils down to concern over other peoples' reactions, and the negative consequences for our own self-image.