One of my teachers asked me to do all 24 etudes from Chopin in 2 weeks. Memorise that is, not play it at concert level. That required around 9 hours a day. The pain after the first day was immense, but the amount of music absorbed great. But I don't really like associating physical pain to music, something which to me inspires only positive emotion.
In the second week, 9 hours was still brutal but did become a little more routine. But to me I think if you push too hard you can end up hating what you are doing. With extreme time pressure, any technical problems you face will irritate you 100 times more than if you had all the time in the world. You can become utterly anxious over sections of music while you try to sleep that you have to jump up and convince yourself that you can do it just so you can get some rest.
So the emotional rollercoaster you go on when you push yourself to the limits can be very tough to manage for people and can turn people off from music easily. I certainly can't maintain 9 hours at the piano a day, even though piano to me sometimes seems like everything, life is just a lot more than just music.
But still i think that if we want to ever gain anything there has to be some form of effort/struggle, that is the same for anything in this world isnt it? Nothing is free! Memorising/playing music is never a walk in the park, we have to always be intelligent in our approach at first. That comes more natural with experience but it is always a challenge at the start. I think if you don't make a commitment to work on problems you face in your music you just won't ever get better.