Such person usually plays both hands and feet together right from the start regardless of the difficulty level of the piece. What happens is that a bunch of mistakes appear and the frustration kicks in.
The irony here is that sometimes we know that it's not correct to practice this way but we do it anyway. Sometimes we are aware of the need to play separate voices at first and combinations of voices later, to master shorter fragments repeatedly first and combine the fragments later but the thing is we are the creatures of habit.
It's really difficult to break that incorrect and inefficient practicing habit and start building something which will last a long time. I guess the real reason often is our inability to believe in the right practice methods and lack of internal faifth in what we are doing.
But there is no other way. We have to realize that only we are responsible for changing our future. Taking action and implementing the right techniques in our practice require guts and will-power for sure but if we want to achieve something which is worth seeking out, something which matters, then we simply have to do it.
There is no point keep doing things in your practice which develop more mistakes. Instead push yourself one step at a time every day a little further in your piece or pieces practicing the right way.
Start a new chapter of your practice. Right here and right now. You won't regret it. From what I hear, so many people have switched to efficient practicing methods little by little.
Never once I met an organist who said, "you know, I applied all of the correct ways of practicing an organ piece. As a result of that, my learning process is much faster and easier now. However, I decided to switch back to my old inefficient studying methods anyway".
No one would say such a thing, right? It's worth the time and effort, although these steps might sound like a really boring thing to do. In just 3-4 weeks, you can perfect your piece you are working on right now AND build a firm foundation for the future practice.