Haste makes Waste
...
I'm sure this happens a lot, in that, my bet is that those that do, are in a rush for whatever, and have either a DA/SA type gun in SA mode, or a SA or DA only, with, or, have a gun with a trigger-job that has been "worked" and it takes but a touch and it goes boom.
Here's what I see happening; in either putting it in their paints, or taking it out, they have their finger inside the trigger guard, or on the trigger, and in their haste, they accidentally waste themselves.
And the golden rule of finger off the trigger, and outside the trigger guard, until you know what your going to shoot, and where the bullet will go if you miss, did not apply.
LS