Exactly, you don't let one shot influence the next one. Because essentially they are no longer relevant to one another. That ball is pocketed and gone and out of the present moment.
Its like trading, one trade does not influence the next. If you just made a great trade, that doesnt mean hold on to a losing/bad trade longer because you have "xtra" money to burn.
Yes Iam guilty of making a great shot and then missing the duck in the same game.

Mainly that is due to treating shots differently. A shot that is hard to make, you take your time, you aim more precisely,etc...Its bad IMO and a disaster for developing a inconsistent game. If you think important shots need extra attention then treat all shots as they are important.
In my particular case, if I try to take my time and give a shot too much attention, I usually miss anyway, because over thinking a shot for me can cause the rhythm in my stroke to go sour.
How many times have you seen a half decent player run a rack up to the nine in 1 minute flat and then miss the nine ball duck. What does that player usually do, they take xtra time (xtra strokes and double check the aim) to pocket that ball because their brain tells them, this shot is really important, yet they just made every shot and shape without thinking twice and did it effortlessly. Or vice versa, they shoot the money ball really fast before the brain has time to send negative possibilities down the pipe.
I have literally heard players say "I have to shoot this fast before I start thinking about it" Its almost profound so say such a thing.... I have tried that shoot fast technique as well, but that too will just add another factor of inconsistency to your game.
Thats why its worth it to have someone else train and watch what you do while you shoot. Someone that has a keen eye, ability to recognize stroking patterns, body language, shot times, every little nuance...