In general, mere repetition (and the concept of it) can be incredibly boring ! If this is the concept of practicing that people are facing when they think about playing the piano, it's going to be really tough to want to do it, and even tougher to get anything of true value out of it. Learning is discovery, not mindless motion. If the concept of practice is boring, the concept needs to be tweaked because boredom is an indication that a process has somehow drifted away from being a discovery/learning experience. Actual learning is not boring at all and is even an adventure (and if it seems that it can be boring, it has become boring only in concept and the concept being linked to meaningless repetition and motion -- so challenge your concept !) !
The main aim with each repetition is to learn something new every time you play it. There are so many different ways to hear it, so many different ways to see it, so many different ways to feel it, so many different ways to conceptualize it -- involve your entire person ! When I approach a new piece of music, my goal in learning it is not just to learn IT, my goal is to learn as much as I can FROM it -- and I think there can be a very big difference in there !
What kind of specific skills do I want to get better at as a musician ? How can I glean from the music-study that I am doing these types of improvements in my musicianship that I am looking for ?
Of course, the type of music a person is learning from is going to have a lot to do with how much they learn ! Something like a Bach's invention, for example, has copious amounts of learning opportunities, whereas some pieces of music do not. Discovering the difference between music that offers substantial learning opportunities and music that does not, is also a skill worth developing. This is how we actually discover what our "tastes" in music are and one way to decide how we are going to be spending our time in study. Once we discover these things, there is really no excuse for boredom because we have the power/knowledge to control that !
The concept of "energy" does play a role, too. I think we all face this ! One thing I have noticed though, is that learning, actual discovery, brings inspiration and energy to a process and it feeds itself. As it turns out, it is much, much more difficult and energy-consuming to resign ourselves to mindless repetition and drag ourselves through time, than it is to act on the decision to learn as much as we can in an allotted time-frame. The decision is our own !
Best wishes,
Karli