There are two problems with safeties. First, none of them is a positive guarantee against an accidental discharge. They are machines, and machines fail. I’ve often heard the claim that it’s safe to carry the Model 1911 cocked and locked with a round in the chamber, because the grip safety and the thumb safety make an accidental discharge impossible. When I mentioned this to my gunsmith, who is also a retired cop, he laughed, and said that he knew of several ADs with the Model 1911 where police had carried the thing in Condition Three and shot themselves in the ass, or the leg, or the foot, or worse, or at least put a hole in a squad car. The amount of engagement on both safeties, he pointed out, is simply not enough to make the gun foolproof.