It was mentioned earlier but we can look at it again.
In the military trials that eventually led to the adoption of the 1911 the Army gave out the weapons for trial to artillery and infantry units and also to the special forces units of the day...the cavalry.
The early guns had no thumb safety or grip safety. The first complaint from the troops was the gun could go off it dropped. So the firing fin was shortened and the firing pin spring made stronger and the grip safety was added. Problem solved.
Next problem, when they were done firing, it took two hands to lower the hammer safely to the fully down position or to the half cock. So the tang of the grip safety was lengthened to allow for one handed de-cocking. Problem sorta solved.
See the horse soldiers were the special forces of the day, they could fight from horseback or ride quickly to the fight, dismount and get into it. They had for decades established the gun handling skills that they always de-cocked their revolvers, both single and double action, before they tried to shove them back into the full flap holsters they carried. Whether it was on the back of a bucking horse or running across a rocky field in the dark they made the gun safe, they de-cocked it, before jamming the gun back in their rig. This lessened the chance of shooting yourself or the horse. That also made it safe to yank out the holster and cock it manually.
The problem they had with the one handed de-cocking was that it was hard to keep the kind of concentration that was involved in doing it safely when running or on the back of a bucking horse. So the thumb safety was added.
The thumb safety meant that you could make the gun safe to jam into a full flap holster while on the run. When you needed to draw the gun again all you had to do was flick off the safety. Easy to do, easy to master.
The thumb safety serves the same function today. With the safety engaged you can with confidence, smack a fella repeatedly in the head, run across a field in the dark, climb a fence, wrestle a fella, jam the gun in a holster while fighting a fella off or grab it out, and more, knowing that as long as the safety's engaged even if the finger strays (and they often do) it won't fire.
tipoc