Here’s my 10p worth as a beginner. I’m logical to a fault, partly to do with my background in Engineering and Quality. So this works for me.
I’m assuming that ‘Lead’ is the horizontal and vertical distance away from the clay that the barrel/shot needs to be, to hit it. Whether it’s perceived lead or actual, that definition works for me. So if the lead is correct I’ll hit it, if the lead is wrong I’ll miss it.
However, the final actual lead given is the ‘effect’. The cause(s) of that effect (the actual lead given) are many and varied. Even with my extremely limited knowledge and experience I can think of several causes.
1) I don’t know how much lead I should be giving it, so it’s aimed wrong.
2) my mount is incorrect so I’m not aiming where I think I’m aiming.
3) the fit is incorrect so I’m not aiming where I think I’m aiming.
4) I’m shooting targets way beyond my skill level and get left behind.
5) I stop just before pulling the trigger, without even knowing it.
6) I look up as I pull the trigger, to see the clay smash.
7) I’m distracted during the process.
8) Fatigue if I’ve done too many clays.
9) eyesight issues (known or unknown)
10) using an inappropriate technique for the clay(s) in question.
I have to say that the books in question have helped me with issue 1). Because of my character I needed a logical, measurable way of understanding it. Gut feel didn’t work in any of my lessons. So I’ve now got a basic way of thinking “it will need about that much”.
However, as a beginner, items 2) to 10) screw me up; sometimes one of them, sometimes multiple. There will be lots more that I haven’t even thought of.
So when I go, I’m trying to get into a very specific process, to do things correctly, consistently. Because to me, ALL of the above must be important.
If I don’t know how much lead to give it, and I do everything else right, I’ll miss. If I do know how much lead to give it and I do other things wrong, I’ll miss. So they all must matter.
I shall now retire to a darkened room, while everyone laughs at the newbie who has got it completely wrong.