The part I found profoundly sad was the “just another day in a glider” low key and low energy conversation in the cockpit. Where this video starts was in an area where great care needs to be taken. Not dangerous per se but there should have been a steady dialogue about how the situation was developing and where the out was as well as some definite “no go” criteria spoken out loud.
The huge one is never fly over a solid deck that is just below you and never ever ever be in a situation where up air is required to stay on top. This goes triple when flying over a ridge. Ridge cloud can develop and/or move very quickly with a change in wind and.has to be respected, as well as the absolute requirement to maintain positional awareness so that you don’t inadvertently cross over to the lee side and get into sink.
Frankly I wonder about the safety culture of this glider club. I find it hard to believe that given the relaxed atmosphere in the glider, that guys where not frequently pushing the ridge lift around and over clouds.
Google “Normalization of Deviance”