Well of course! Anything with excessive repetition gets annoying and can lead to a ''burn out''. I mean, lets take your brain as an individual person. You start teaching him something slowly and he starts to get it. At one point he got it but you keep on repeating to him the same thing over and over again and at one point, he is not stimulated anymore. He got the point but now you keep repeating it to him!
That's where the break is important, once the brain is saturated, and the links have been made in the neural system and motor skills, the brain will then relay it to those and move on to something else.
That's why a lot of people can play something fast and it seems like they are not struggling with it. Because the truth is, they aren't even thinking about it at this point. The muscles took over and they just know what to do because that is what they have been trained to do! And that's why often, if you start thinking too much about you are doing, you are going to start failing more. I like to think of it as the brain meddling over in the muscle memory system and not allowing them to do their job properly.
In other words, imagine a boss constantly coming in to check over that you are doing your job properly but by asking you if its up to performance all the time, it distracts yous and you can do it a full capacity!