When I joined college I was a pretty bad swimmer. During freshman year I took some beginner/intermediate swimming classes and learned proper swimming technique for stomach crawl, breaststroke and butterfly. The next year I saw this class called Master’s swimming, spoke to the coach and signed up for it. I was by far the weakest swimmer in the class. Everybody else had great stamina and technique. We would do series of 50 metres swimming for 50 seconds and then 10 seconds break until the next series. In the course of an hour others would cover around 3km. In the beginning I had such a low stamina I would barely make it past 1. 5km per practice.
I thought that the coach would tell me to switch to a less demanding class, but to my surprise he never did. Instead he gave me advice how to swim better. Some of his advice was about the technique- “keep your head low when you breathe”, “insert your hand at an angle when you swim crawl- it takes less energy”. But he also had some mindset advice which I think generalizes very well to other parts of life -“When you are tired focus on performing your technique correctly” and “Frequency is more important than intensity [of the workout] “
At the time, both of those advices were counterintuitive to me. When I was tired I would preserve my energy by being lazy, half-assing my technique and slowing down, barely surviving through the rest of the practice. I thought this wasn’t that bad but the coach got me corrected. When I practiced with improper technique my movements would get worse and worse over time as the improper technique becomes the norm. As I focus on technique, it helped get my mind off the tiredness, and also conscously think about exactly what I was doing. Surprisingly, this also improved my technique even in cases where I thought I had it figured out.
Regading his second advice, that the frequency is more important than the intensity, I noticed that by going regularly to practice (which for me was twice a week) I would get in a better shape and be able to swim 2+ km per practice. It would also make it easier to keep improving as it would be easier for me to pick up from where I left off. Without regular practice even if we focus on doing quality effort we get off-shape and our muscles atrophy. Thats why I think that the second advice, that frequency is more important than intensity is stronger advice than the first one- focusing on correctness.
Focusing on correctness could also be possible in situations where it is not very clear what correctness means, but some feedback is available - in this case I would consider regular practice plus feedback to be a better way to learn and improve.
I’ve read of this study  that asked students to make as good of a clay pot as possible. The students were divided into two groups, the ones in the first would make a new pot every day, while the ones in the second would work on one pot for fifty days to reach perfection. The kids that did a new pot everyfday outperformed that were perfecting their single pot. Their pots had better quality.
Did the students in the second group only cared about completing their daily assigned pot? But also they had self produced feedback - they could look at the differences in their process and in their results from day to day, learn what makes for better results and improve. They had the benefit of being able to start anew and thus not getting stuck with bad choices. If they thought there was a better design they were free to try it. Going for quantity won over going for quality alone; frequency won over intensity.
Practicing regularly collects a lot of examples and experience for our brains to learn from. The more varied the experience the better the learning. Focusing on correctness when tired, when reaching our physical or knowledge limits allows us to generate more informative experience, bringing more clarity and skill.
Whenever, I’m trying to get good at something I try use these m advices for guidance - “frequency is more important than intensity”, and “focus on doing it correctly”, even though it might feel slower or more painful. There is the hope and the promise that after enough repetitions i will get good at it, just as the kids who built the clay pots got good at them. Starting small and not worrying about perfection helps me keep the frequency high until I gradually improve to the point where I can start focusing on correct technique.