I'm probably not willing to put in more than an hour a day. Trying to explain it to my friend helped me understand the process better. If something is too hard -- that is -- I don't have the skill set for it, it is like trying to lift 50 pound weights. If I am used to doing 5 to 8 pound weights for 20 reps at a time, no matter how much I "practice", I'm not going to be lifting 50 pound weights anytime soon.
Another example, I gave was, that practicing the cello is like running a marathon. Playing an instrument not only requires knowledge and musicality, it's also very physical. Playing too much hurts if you're not used to it.