But that is not how people are normally trained. Normally people are trained in safe conditions where participants know they are in a training session.

You put people in unnecessary danger by putting them in an unpredictable situation. That is why training sessions are varied and thoroughly debriefed so that participants can know how what they learned in the current session can be applied at different settings.

Source, anecdotal: I’m a former life guard that had regular drills, and never entered one unknowingly.