A Metaphor:
You wish to carry a large dresser up the stairs. You can choose to make several trips by taking each of the drawers out, or you can try to wrestle the whole thing in one go.
A motto:
practicing is not doing something over and over until you get it right...Practicing is doing something RIGHT over and over. Remember, your performance is the sum total of what happens in the practice room.
Here's the difference. Let's assume you are looking at a new goal (measures 9-12 left hand only) that you wish to practice, and eventually pass a test...your goal is to learn the entire section without making even one mistake in the process.
The only way for this to be possible...is to look for the simple withing the difficult. Start easy, and gradually add difficulty. play slow, work on smaller sections, and of course Hands together. I will give my two favorite other simplification tools---tapping (isolating only the rhythm)---and pulsing (playing only strong metrical beads first, then filling in the rest)
Here's one possible sample approach that can actually allow you to not even make one mistake while practicing:
1) count out loud and tap the rhythm 5x (use left hand on left knee...this actually initiates the neuromuscular reference point in your subconcious...it is very important that the first three repititions be accurate
2) take Left hand from one measure to the next, trying to find a position on the keyboard that allows you to play each measure with ease. Just touch the keys in the best 5 finger position
3) Scour the section looking for intellectual reference points. All rudiments, motifs, sequences ect should be identified and labeled. (you have not played even played a note yet...don't worry it will come soon)
4) While looking at the score, imagine yourself playing the music, internally feel any spots where fingering may be a challenge. work them out now without making a sound. (this will help you to develop a 6th sense with fingering)
5) PLAY only the first beat of each measure. Then add any other metrically strong beats (3) if in 4/4. Finally add in any other filler notes. (use a slightly larger muscle initiation for the strongest beats---upper or lower arm---). A push, like a ice skater. This will help to feel comfortable as you sense the spaces in each measure.
6) Play through a few times normally
7) Test yourself with the metronome, 3x in a row to pass. The speed is not important, after all, if your technique is solid, any memorized, internalized material will be comfortable at your max technical level.
Remember that your concentration lives and thrives in the land of the possible. Practice with a sense of ease. Linger on each of these steps longer than you normally would.
Could you learn it faster by just jumping in Hands together, playing normally? Often you can...but you will have played it ONCE correctly instead of 50-100 times correctly using my approach. This approach has a learning curve in it's application. You are learning how to learn

I understand how this sounds.
Some cannot be bothered to go through all of this. I cannot be bothered to wrestle with a slippery subconcious later on when I have to painstakingly clean up the mess that is left there from the plethora of accurate and innacurate information that is juxtaposed there.
If you make it through the practice process without one mistake (I've come close, but never managed it...YET). I sincerely believe that you will not be able to make a mistake in performance even if you tried.