Sighting and reassurance
When you are standing upright over the shot you are computing all that needs to be done.
The contact point to pocket the ball. (square up) (Sighting in)
Where your next position is.
Obstructions etc.
English if any is required to get that position.
Type of stroke and speed to get that position.
After all that is completed, which should not take all that much time unless you have a tough play you are ready to go down on the shot.
When you drop down into the shot your cue should be 99.9 % or better in line to pocket the ball, if it isn't it is such a small adjustment it usually can't be detected unless someone is behind you staring down the cue.
From the upright position to down on the shot your perception changes.
By dropping the cue on the cloth you are basically taking it out of your sight
(YES I said that,,Out of your sight)
What that does is clears the line for your eyes to adjust to the change in perception. Your cue is already 99.9 % or 100 % in line, if not you make such a small adjustment (the thickness of hair may be all you need) it only takes a second
I do this on every shot no matter what the difficulty is. English, power, high follow, slow roll ETC...It doesn't matter
Try This...go thru your pre-shot routine, once you are down on the shot have someone take the cue out of your hand or just slide it out of your way without taking your eyes off the cue ball and object ball and not moving from your ready position...all you will see is the Cb and Ob.
You have reassured your sighting and corrected any aiming with the cue stick almost subliminally.
Sorry,long post and I didn’t cover it all, wind is up and I am not out fishing today.
This was taught to me and basically explained the same way from a few players who are no longer with us. World Champs