Same thing that happens when you mark the wrong place on a ruler, bad input bad output, you miss.
I find that the two line process makes it hard to misjudge initial perception.
It's like saying well what if the shot is a half ball hit and you are at 7/16th but think you're at half ball. You know the shot is a half ball hit so you work on your vision until you know exactly what a half ball hit looks like to you. Then you have a constant reference that allows you start being accurate with connecting the objective references, center and edge to the subjective references quarter-lines, in an objective process.
The shooter goes from I think it's there to I know it's there. Confidence in the choice is the key here.
As Grady Matthews used to say, "I have never been beaten by a player who thought he could play, only by the ones who knew they could play".