Lots of explanations that are saying essentially the same thing.
However, if the proper sight picture is on the target when the gun goes bang, you hit. Or if the shot goes somewhere else, it's a sight problem.
A friend was shooting low, as usual. He said, "jeez, the sight was right there when I shot." I explained that it was not. "Your sight was right there when your brain said shoot. By the time you shot, it was not because you gave up and quit. Keep the shot on target until the shot breaks. Do that by concentrating on it."
Then, when I'd shoot low, he tell me the same thing. And he was right. We all do it. Knowing what we did is what's important.