One great example:
Junior folks kept hitting the wrong buttons during safety evaluations so the crew instituted a "positive action" e.g. "I am about to turn on this device" before they did anything.
During the safety review, the reviewers came back and said:
"You performed fewer errors than anyone we've ever tested. Actually, we take that back, your crew was ABOUT TO make as many mistakes as normal but the verbal call out meant that everything was double checked leading to such a lower error count"