Speaking from experience here, shots that are incredibly lucky happen a lot more often that it seems they should.
I once hit a 1 inch wide steel target at 250 yards with a .22 with pen sights. No spotting shot, just set the elevation and fired. Everyone heard the faint clang from the hit and no one could believe it. I felt really good about it for about an hour, then I tried it again. Everything was the same but I hit 15 feet low, right next to a little, flat rock. Best guess is the first shot hit that rock and bounced the bullet up into the target.
My dad once aimed at the cap a 1 gallon milk jug only to graze the side of it, unscrewing the cap.
I've also hit a pumpkin at 100 yards with a .22 derringer pistol. This is gun so small that my girlfriend can't shoot it. Her index finger (which lays down the side of the barrels while the trigger is pulled with the middle finger) is longer than the barrels. The pumpkin shot was the first try as well.
In Bowling Pin Shoots, competitions where the goal is to clear 5 bowling pins off of a sheet of plywood at 7.5 yards as fast as possible, I've seen many people get 2 pins with one shot when the bullet sticks in the side of one pin, then it flies out when after the pin rotates a bit. Yes, the bullets sometimes come back at the shooters. One guy hit himself in the forehead. It had slowed down a lot, but it still hit pretty hard.
All of this has taught me two things. It is possible for some incredibly farfetched thigs to happen, so no single example of a difficult shot should ever be taken as standard. And if such a shot ever happens, smile like you meant for it to happen, set the gun down and never, ever try it again. At least not in front of witnesses
