As a long time instructor I'll concur with the stress induced performance failure(s).

One other point that is really relevant here - as an instructor we have to ensure that we don't place the student on a pedestal thinking that he/she is a "top" competition pilot or the wisest and most experienced pelican around so "of course he/she knows what they are doing, I'll just assume...." and sit back while they auger it in.

An experienced instructor can tell pretty quickly in a simulated (or actual I guess) emergency or abnormal situation if the pilot understands, is coping well and if the situation is going to end wrong. It is incumbent on the instructor to allow the lesson to be learned without allowing the end result be in question. Always a tough balancing act but I know from experience, it doesn't matter how much of a "top gun" pilot this student is - she/he might be rusty, out of practice on these maneuvers/procedures, might have developed bad habits, might be used to flying a different glider (maybe only one ship for many years only getting out of it once every two years for a flight review), flies a 50:1 glider normally and is doing the review in a 34:1 ship, maybe is not used to flying with someone else, may have had a massive stroke on base leg - whatever the cause the CFI has to be on their game and prevent a horrible end result.

I know of too many of these stories that end badly, have had some scares myself. Seen it in power, gliders, commercial operations - it's a "gotcha" for the instructor.

I think very carefully at the purpose of each maneuver, the risk/benefit, the value of the teaching moment and the entire battlespace - what is happening in the pattern and so on. High risk, low reward simulated failures have to be analyzed, managed and often after evaluating are probably not worth it. We used to do some really macho stuff in multi-engine training years ago that killed quite a few people both in training and then in practice - most of us learned and adapted.

Regards, Tom