It is clear that assigning blame most of the time does not create a solution. There is even a bigger chance that a similar future situation will have the same result. First of all because the person who made the mistake the first time, is not allowed to do it a second time. And so has no chance to practice what he learned from the first time. Secondly, because the person who did it wrong the first time, is afraid to make a mistake again and so makes new mistakes.
The first situation is only solved by giving the maker of the mistake another try. That needs trust on both sides that this time around everything will go right. To create that trust, you could have a good talk about how the job will be done. The danger of a good talk however is, that the plan will be that of the one who has the greatest need for trust. And most often that is the client, who was disappointed the first time. Such a plan however is not trust, but control. So the art of these good talks is to find the middleground. Trust in the plan is created, without the plan becoming a way of control.
In the second situation the goal will be to prevent or take away any fear of making mistakes. Preventing should not be that difficult. That is often no more then not finding blame, but looking for solutions. The only two things that need to be done to achieve that is not talking about someone, but talking about what should be achieved. So not a person should be the topic of the talk, but the activity. The point is, that blaming does not bring or create a solution. But talking over possible solutions does. An additional advantage of a talk about solutions, is that the producer of the mistake will get a chance to reflect on what went wrong and what can be done to do it right.
You will have a real problem, when the person who is going to do the job, is afraid to make mistakes. It can be a result of the reaction of the judge. But it can also be the result of past experiences. In that case however, the only person who can do anything about it, is the person who is afraid.