For me, it has to do with running out of mental gas.
Focus is a limited resource and I blow a lot of that resource in the first 6-7 balls trying to play perfect shape and cinch every ball. By the time time I'm on the 8 or 9 I'm mentally tired of bearing down and just want to finish up and get out.
When you see strong players who have a quick pace and seem to get out of the rack like it was simple, I think part of what makes them successful is they don't blow their mental wad overthinking the first half of the rack. They conserve their mental energy on the roadmaps, and save it for the situations that need it.
And now for something completely different:
How often does it seem like the end of the rack looks like this? For me, it feels like all the time... even when the racker is trying to be random.
The shot is a little tricky because you need a little inside spin, and have to worry about scratching in the side. Lots can go wrong... you hit it a little weak and end up near B. You overhit it and end up near A. Your spin doesn't take and you end up dead center of the table, where you can cut the ball in either corner.
See if you notice this shot coming up a lot for you. When it does, take a second to understand: this is probably the hardest shot in the whole rack. Maybe you dog the 8 because it was actually harder than any other shot... it needed lots of CB travel, some force, and some spin to get good on the 9.
In fact, if you think about it, the way 9 ball rack works maybe makes it naturally difficult to get good on the 9. When the balls are racked well, it doesn't move much. Realistically you only want to shoot it in the bottom corners though it goes in all six pockets. So it seems like to get good on the 9, you must send the cue ball towards the side pockets. Imagine for a second that you had the "other angle" on the 8 ball, i.e. the cue ball starts a bit below B. You can definitely scratch in either side depending on how you hit that ball. But if you take pains to avoid that, you also risk getting tough on the 9.
OK, long post, here's the summary:
1. If the rack is a roadmap, try picking up the pace on the early shots and just let them become automatic. Save your mental energy for the critical balls at the end.
2. If you find yourself in the diagrammed position a lot, practice shooting with just these two balls, and figure out how to hit this so you don't risk scratching and get good on the 9. Make this shot your "pet shot" that you never ever screw up.
3. Random tip that has worked for me: Shoot the 9 with a deliberate, 100% natural, unthinking stroke. Do not hit the ball with a shortened bridge, or a 'cinch stroke', hit wherever you like on the cue ball (a little outside if that's your habit... or just below center, or just center) ...don't fret about shape (except to avoid a scratch). Just hit it with slow, firm stroke, with nothing in mind but drilling it in. Don't think about how your funny banana stroke or whether your elbow is moving or whatever. Basically I try to imitate shane when I'm hitting the game ball, because pretty much all of his strokes have that slow, deliberate look. Trust your stroke 100%.
Focus is a limited resource and I blow a lot of that resource in the first 6-7 balls trying to play perfect shape and cinch every ball. By the time time I'm on the 8 or 9 I'm mentally tired of bearing down and just want to finish up and get out.
When you see strong players who have a quick pace and seem to get out of the rack like it was simple, I think part of what makes them successful is they don't blow their mental wad overthinking the first half of the rack. They conserve their mental energy on the roadmaps, and save it for the situations that need it.
And now for something completely different:

How often does it seem like the end of the rack looks like this? For me, it feels like all the time... even when the racker is trying to be random.
The shot is a little tricky because you need a little inside spin, and have to worry about scratching in the side. Lots can go wrong... you hit it a little weak and end up near B. You overhit it and end up near A. Your spin doesn't take and you end up dead center of the table, where you can cut the ball in either corner.
See if you notice this shot coming up a lot for you. When it does, take a second to understand: this is probably the hardest shot in the whole rack. Maybe you dog the 8 because it was actually harder than any other shot... it needed lots of CB travel, some force, and some spin to get good on the 9.
In fact, if you think about it, the way 9 ball rack works maybe makes it naturally difficult to get good on the 9. When the balls are racked well, it doesn't move much. Realistically you only want to shoot it in the bottom corners though it goes in all six pockets. So it seems like to get good on the 9, you must send the cue ball towards the side pockets. Imagine for a second that you had the "other angle" on the 8 ball, i.e. the cue ball starts a bit below B. You can definitely scratch in either side depending on how you hit that ball. But if you take pains to avoid that, you also risk getting tough on the 9.
OK, long post, here's the summary:
1. If the rack is a roadmap, try picking up the pace on the early shots and just let them become automatic. Save your mental energy for the critical balls at the end.
2. If you find yourself in the diagrammed position a lot, practice shooting with just these two balls, and figure out how to hit this so you don't risk scratching and get good on the 9. Make this shot your "pet shot" that you never ever screw up.
3. Random tip that has worked for me: Shoot the 9 with a deliberate, 100% natural, unthinking stroke. Do not hit the ball with a shortened bridge, or a 'cinch stroke', hit wherever you like on the cue ball (a little outside if that's your habit... or just below center, or just center) ...don't fret about shape (except to avoid a scratch). Just hit it with slow, firm stroke, with nothing in mind but drilling it in. Don't think about how your funny banana stroke or whether your elbow is moving or whatever. Basically I try to imitate shane when I'm hitting the game ball, because pretty much all of his strokes have that slow, deliberate look. Trust your stroke 100%.