I may have related this anecdote before...
Having coffee, and perusing the Denver Post, one morning many years ago, I read of a Rocky Flats (former Tritium/nuclear weapon site near Golden, CO) security force officer shooting themselves in the foot while on duty at Rocky Flats. I rolled my eyes at the obvious stupidity...
Later that week, I stopped by my neighbor's house. Great guy, who will remain nameless, who worked at Rocky Flats as, you guessed it, a security force officer.
He came to the door on crutches...with a cast over his foot...
And I awkwardly realized who the "shooter" was...and he told me what happened. They had just been issued new Glocks to replace their Sigs. But the force hadn't received their new holsters. So, they were directed to carry the Glocks in their old leather. While driving a pickup truck on a perimeter patrol, his weapon came loose and he...yep...THUMB-CHECKED it back into the holster. Safe, right?
Except that thumb-checking makes no difference on a Glock, and the Glock's trigger caught on the leather of the Sig holster, depressing the trigger safety, and the trigger, and a round discharged, grazing his thigh, and going through his foot.
I blame his supervisor who sent him out with inadequate gear. New gun in an old holster? Really?
But, I suppose the moral of the story: thumb-checking, while a good habit on a hammer-fired pistol, does little to keep you safe with a striker-fired pistol. That, and, never carry a gun in a holster designed for another gun.