And you misunderstand the whole anxiety issue. It's easy to say "stop caring and just do your job / stop worrying". The deal for many - actual - anxious people is: They are likely quite aware of all that. They are aware that in retrospec all nervousness and panic was exaggerated. Depending on which degree the "anxiety" is, you just can't control it. You can self-suggest yourself it's fine, but it may or may not be enough. For "outsiders"/bystanders, the whole deal with anxiety seems quite absurd (and sometimes so it feels for the persons affected ironically), yet if it were for them so easy to dismiss, they would easily be able to "cure" themselves.
But I agree, normally all nervousness lessens or can disappear over time. Mistakes happen, especially if you don't run (or want to) run each dungeon ad nauseum, and nobody will likely care in the long run.