When you want to become a better, more serious runner, you often need to change the way you run. The same goes for swimming. If you work with a coach, they will watch your stride or stroke and then work with you to change the angle you are putting your foot down or of your arm. This is difficult and annoying.
It also results in your speed slowing down. It requires your brain to be very present with the muscles in your body and consciously change how they work. This is slow. You have to unlearn and relearn. For a while, you get worse at running or swimming, but if you stick with it, there are long term benefits as once you learn how to run or swim properly you reach a whole new level.
The same idea applies to swinging a golf club, baseball bat, cricket bat, and shooting hoops or kicking a football (soccer ball).
But it also applies to many innovation and change projects. The new process or way of doing things is clunky, slow, annoying. Our revenue or performance drops for a while, but picks up in the long term. Expecting immediate ROI is unrealistic, short-term-ism, and silly.