Training with new gear and being consistent
There is no debate about firearms safety, you either follow the rules or you will have an accident. The problem with fireams training is everyone has an off day, not everyone wakes up in the morning and is at 100% mentally there. Everyone trips or falls at some point, every slips on the ice they didn’t see and not everyone can think straight until they’ve had their cup of joe. I’ve seen more accidents with Glocks than any other sidearm, but I would say that Glocks are the most reliable firearm I’ve seen at training courses.
One thing that I have seen happen with gun owners, is they juggle firearms around too much. It really is not a good idea to switch up your holsters and firearms too often because mental lapses can occur. This seems to be the problem people are having with the Blackhawk Serpa holsters that are getting on the news. If you don’t use this holster all the time, you may have a problem keeping your hand in the same spot and you’re more prone to curling your finger and causing an ND. I very much like the retention design and the strength of the holsters, but I would not let a novice shooter start out with one.